ISSN: 0895-8378 print / 1091-7691 online DOI: 10.1080/08958370490439579
Effects of Concentrated Ambient Particles on Heart
Rate, Blood Pressure, and Cardiac Contractility
in Spontaneously Hypertensive Rats
Chuen-Chau Chang
Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University, Taipei, and Department of Anesthesiology, China Medical College Hospital, Taichung, Taiwan
Jing-Shiang Hwang
Institute of Statistical Science, Academia Sinica, Taipei, Taiwan
Chang-Chuan Chan
Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University, Taipei, Taiwan
Peng-Yau Wang
Graduate Institute of Environmental Engineering, National Central University, Chung-Li, Taiwan
Tsuey-Hwa Hu
Institute of Statistical Science, Academia Sinica, Taipei, Taiwan
Tsun-Jen Cheng
Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University, Taipei, Taiwan
Epidemiological studies have shown that particulate matter (PM) air pollution is associated with cardiovascular mortality and morbidity, especially for particles with aerodynamic diameters under 2.5µm (PM2.5). Recent studies have revealed an association between PM pollution and
autonomic functions including heart rate (HR), blood pressure (BP), and heart-rate variability. However, the association and linking mechanisms have not been clearly demonstrated in animal studies. Utilizing a novel approach that employs a mixed-effects model to overcome the prob-lems of variations in diseased animals and circadian cycles, we have previously demonstrated an association between concentrated PM2.5and changes of HR and BP in pulmonary hyper-tensive rats. The objective of this study is to test the plausibility of this methodology and to demonstrate the particle effects under different pathophysiology. The feasibility of cardiac con-tractility (measured as QA interval, QAI) as an indicator for PM toxicology was also explored. Four spontaneously hypertensive (SH) rats were repeatedly exposed to concentrated PM2.5 dur-ing sprdur-ing and summer. The mass concentration of particles durdur-ing the 5 h of exposure was 202.0± 68.8 (mean ± SE) and 141.0 ± 54.9 µg/m3for spring and summer experiments,
respec-tively. During spring exposures, the maximum increase of HR and mean BP noted at the end of exposure were 51.6 bpm ( p< .001) and 8.7 mm Hg ( p = .002), respectively. The maximum
decrease of QAI noted at the same time was 1.6 ms ( p= .001). Though a similar pattern was demonstrated during summer exposures, the responses were less prominent. We conclude that concentrated PM2.5may increase HR and mean BP and decrease QAI in SH rats. Our results also show that QAI may be used as an indicator in PM toxicology.
Received 11 June 2003; sent for revision 26 June 2003; accepted 9 July 2003.
The authors are grateful to Ming-Chih Chen and Yu-Chen Lei for their technical assistance. The authors also thank the National Institute of Environmental Analysis, EPA, Taiwan, for its administrative support (funded by EPA-91-FA11-03-91DF02).
Address correspondence to Dr. T.-J. Cheng, Institute of Occupational Medicine and Industrial Hygiene, College of Public Health, National Taiwan University, 1 Jen-Ai Rd. Sec. 1, Taipei, Taiwan 100. E-mail: tcheng@ha.mc.ntu.edu.tw
Increased concentrations of ambient particles are associated with cardiovascular morbidity and mortality in many epidemi-ological studies (Pope & Dockery, 1999; Samet et al., 2000). Research has also indicated that particles with aerodynamic di-ameter less than 2.5µm (PM2.5) exert greater adverse health effects than coarse particles (Pope et al., 1995). However, the mechanisms of such associations have not yet been clearly de-fined. Recent epidemiological studies have found associations of increased air particles with increased heart rate, blood pres-sure, and arrhythmia, and with decreased heart rate variabil-ity (Peters et al., 1999, 2000; Pope et al., 1999; Gold et al., 2000; Ibald-Mulli et al., 2001). Activation of autonomic ner-vous system (ANS) has been postulated to play a role in these relationships (Stone & Godleski, 1999). To further clarify these relationships, animal models have been used to investigate the effects of particles on heart rate and blood pressure (Godleski et al., 1996; Kodavanti et al., 1998). Results of the prelimi-nary studies, however, were inconsistent (Godleski et al., 1996; Watkinson et al., 1998, 2001). This is probably due to the in-adequacy of the experimental designs. Because of the wide variation among diseased animals and circadian cycle of hemo-dynamic parameters, a large number of animals is usually re-quired to delineate the true effect of air particles (Kodavanti et al., 1998). To overcome this problem, we successfully used self-control design and a mixed-effects model to detect the ef-fects of particles on heart rate and mean blood pressure (MBP) in three pulmonary hypertensive Sprague-Dawley (SD) rats ex-posed repeatedly and alternately to concentrated ambient par-ticles (CAP) and filtered air (Cheng et al., 2003). In order to further clarify the plausibility of the methodology and the par-ticle effects under different pathophysiology, we used a sim-ilar tactic to investigate the effect of concentrated PM2.5 on
heart rate and MBP in spontaneously hypertensive (SH) rats in this study. A recent study had observed exacerbated cardiopul-monary injury and oxidative stress in SH rats exposed to PM. The study concluded that SH rat is a potentially useful model with susceptibility to cardiovascular diseases (Kodavanti et al., 2000).
Cardiac contractility is under close modulation of ANS func-tioning (Kent & Cooper, 1975; Kawano et al., 2003), and thus is likely to respond well to CAP exposures, since ANS responses have been postulated as an important mechanism linking CAP and cardiovascular toxicity. Using QA intervals (QAI) as an in-dex of cardiac contractility, the feasibility of applying cardiac contractility to the PM toxicology was also explored in this study.
MATERIAL AND METHODS
Animals and Development of Systemic Hypertension Sixty-day-old male SH rats were obtained from the National Laboratory Animal Breeding and Research Center in Taiwan. Housed individually in cages with Aspen chip bedding renewed twice weekly, the SH rats were provided with PmI/LabDiet
5001 and water ad libitum except during the PM exposure peri-ods. A 12-h light/dark cycle, a constant room temperature of 22 ± 1◦C, and a relative humidity of 55± 10% were maintained in
the animal room during the study. Owing to the genetic makeup of SH rats, a systolic pressure over 150 mm Hg develops spon-taneously by the age of 5 wk, and is maintained thereafter at higher levels (Okamoto et al., 1974).
Experimental Design
Four SH rats were implanted with radiotelemetry transmit-ters (model TL11M2-C50-PXT, Data Sciences International, St. Paul, MN) at the age of 10 wk. Two weeks for surgical re-covery was allowed before baseline data collection. Baseline data consisting of ECG and aortic blood pressure signals were collected on unanesthetized, unrestrained animals, over a period of 1 wk before CAP exposure in both the spring and summer.
Ambient particles in the Chung-Li area, a suburb of Taipei, were concentrated by a modified ultrafine particle concentrator (UFPC) (Sioutas et al., 1999). Ambient particles were carried by a major flow of 110 L/min to a warm-water bath for over-saturation, and grown in a cooling condenser, selected by a virtual impactor, and recovered to their original aerodynamic diameters between 2.5 and 0.01µm by a diffusion dryer. The UFPC produced a negative pressure of around 2 mm Hg inside the nose-only exposure chamber with an output minor flow of 10 L/min. A condensation particle counter (CPC, model 3022A, TSI, Shoreview, MN), located on both input and output arms, was used to analyze the particle concentrations before and after UFPC for every 30 s. Placed in one of the two output arms, polycarbonate filter paper was used to collect the particles for mass concentration calculation.
Experiments were conducted on Tuesdays and Thursdays in the spring, and on Mondays and Thursdays in the summer. There were 4 days of exposure in the spring season, specifically, 26 and 28 February and 5 and 7 March 2002, and 6 days of exposure in the summer, namely, 6, 13, 17, 20, and 27 June and 4 July 2002.
On the days of the experiment, about 1 h of accommodation (10:00 to 11:00) in closed-type animal holders (model CH-2500, CH Technologies (USA), Westwood, NJ) was allowed before the animals were fitted to the connector cones of nose-only exposure system (12-port nose-nose-only modular, CH Tech-nologies) at 11:00. Two SH rats were then exposed to CAP (exposure group), while the other two were exposed to HEPA filtered air (control group) for 5 h (11:00 to 16:00). SH rats served as exposure and control group alternatively.
Heart Rate, Blood Pressure, and Cardiac Contractility Measurements
With the radiotelemetry system, all signals throughout the study were collected on a continuous basis. The sampling rates for the electrocardiograph (ECG) signals were set at 1000 points per second (1000 Hz) for better temporal discrimination, and 500 Hz for blood pressure signals. Parameters including
electrocardiograph (ECG)-derived heart rate (HRE) and mean blood pressure (MBP) were retrieved from the system at 10-min intervals.
Cardiac contractility was measured by QA interval (QAI), which was defined as the time duration between the Q wave in the ECG panel and point A (pressure upstroke in aortic pressure) in the pressure panel, in units of milliseconds (ms). QAI was automatically calculated by the system, and the 10-min means were output as a parameter.
Statistic Analysis
Owing to low-power effects in the fourth SH rat during sum-mer experiments, a decreasing trend of MBP data was observed for the last 3 wk before signal transmission went out completely. Time duration data, including HRE and QAI, were not affected at the same time. The MBP data during summer experiments of the fourth SH rat were then excluded from statistic analysis. The three measured parameters, HRE, MBP, and QAI, were classified into three groups by experimental conditions of expo-sure group (exposed to CAP), control group (exposed to filtered
FIG. 1. The averages of crude effects across all SH rats plotted against clock hours. Spring data are shown in the left column, and summer in the right column. Data of HRE are in the upper panels, MBP in the middle, and QAI in the lower panels. Baseline group data are shown in dotted lines, control group in dashed lines, and exposure group in solid lines.
air while staying in nose-only exposure system), and baseline group (exposed to room air during baseline period). Each rat’s circadian baselines in the two seasons were separately estimated using hourly means of measurements obtained from its base-line data. The circadian basebase-lines were then subtracted from the HRE, MBP, and QAI data for the corresponding hours to obtain crude effects for each rat in the two seasons separately.
The average crude effects of all SH rats in baseline (dotted lines), control (dashed lines), and exposure (solid lines) groups plotted against clock hours are shown in Figure 1. The average crude effects for baseline group are around 0, showing no cir-cadian pattern. During the preparatory stage of 10:00 to 11:00, SH rats stayed in animal holders for accommodation, and the average crude effects in HRE and MBP for both control group and exposure group increased from the baseline condition ow-ing to mild stress. At the same time, QAI decreased durow-ing this preparatory stage. The chamber effects, denoted by the crude effects of control group data, developed as the SH rats entered the animal holders, and gradually diminished to some extent through the course of the inhalation stage from 11:00
FIG. 2. Hourly means and estimates of PM effects. Spring data are shown in the left column, and summer in the right column. Data of HRE are in the upper panels, MBP in the middle, and QAI in the lower. The hourly means (×) are smoothed by robust locally linear fits after exposures (smoothed curves after 16:00). The estimates (—) and 95% confidence intervals of the PM effects during exposure (11:00 to 16:00) are obtained from mixed-effects models.
to 16:00. The chamber effects peaked at 16:00 as the animals were released from the nose-only exposure system and returned to baseline conditions within hours after the experiments (af-ter 16:00). The differences between crude effects of exposure group and control group were defined as the PM crude effects. The average PM crude effects, as shown in Figure 2 by× sym-bols, evolved during the inhalation stage and also returned to the baseline condition after the end of the experiment.
We used a linear mixed-effects model to further examine the PM effect during exposure. Chamber effects and PM effects were both modeled with a set of dummy variables. There were 6 dummies for chamber effects and 5 for PM effects, each stand-ing for 60-min estimation. Let Yiktbe the crude effect for the i th SH rat in the kth condition (0 for baseline group, 1 for control group, 2 for exposure group) at time t (1 to 6 for each 60-min
section during the 6 h of the experiment). The mixed-effects model is given as Yikt = 6 m=1 (ami+ αm)I (INikm) + 5 m=1 (bmi+ βm)I (PMi k(m+1))+ εikt
where I (INikm)= 1, when the ith rat was in the chamber during the kth experiment at the time t= m(m = 1–6) and 0 otherwise,
I (PMi k(m+1))= 1 when the ith rat during the kth experiment was receiving CAP at the time t= m+1(m = 1–5), and 0 otherwise. The error termεikt was chosen to be an autoregressive process with order 2 to model time dependence. The coefficients ofαm,
for m = 1 to 6, were used to describe the hourly mean fixed chamber effects during the 6 h of the experiment. The dummy variablesβm, for m= 2 to 6, were used to describe the 60-min mean fixed PM effects during the 5 hr of exposure. Since the four SH rats were randomly selected from a population, we added random components amiand bmito model the rat-to-rat variation of these effects. All these random coefficients were assumed to be normally distributed with the mean of 0 and some constant variances. We used S-Plus to estimate the parameters and standard errors of the estimates in the model.
RESULTS
Condensation particle counter (CPC) readings showed an average preconcentrating particle concentration of 1.59× 104
(range: 5.28× 103 to 5.08× 104) particles/cm3 and a
post-concentrating level of 2.30× 105(range: 7.12× 103to 8.26× 105) particles/cm3, with an average concentrating power around 14 for the spring experiments. Concentrating power by CPC for summer exposures was around 17, with an average pre-concentrating particle concentration of 1.59 × 104 (range: 2.90× 103 to 1.21 × 105) particles/cm3 and a
postconcen-trating level of 2.78 × 105 (range: 7.76 × 103 to 8.87×
105) particles/cm3. Gravimetric analysis revealed the
post-concentrating mass concentration of particles during the 5 h of exposure of 202.0 ± 68.8 (mean ± SE) µg/m3 for the
spring experiments and 141.0± 54.9 µg/m3 for the summer
exposures.
The crude effects of HRE (upper panel), MBP (middle panel), and QAI (lower panel) are plotted against clock hours in Figure 1, with data from the spring experiments showing on the left-hand column and those from summer on the right. All the SH rats were fit into closed-type animal holders and ac-commodated from 10:00 to 11:00. The animals were mounted in the nose-only exposure system and started to receive CAP (for exposure group) or filtered air (for control group) at 11:00. As used for the baseline template, the crude effects of baseline group (dotted lines) oscillated around zero with no significant trend, justifying the appropriate removal of circadian trend. Ef-fects of the control (dashed lines) and exposure (solid lines) groups evolved through the course of the experiment. During the preparatory manipulation from 10:00 to 11:00, the crude ef-fects of HRE and MBP increased while that for QAI decreased owing to mild stress. Similar patterns of increased HRE and MBP, together with decreased QAI, were also observed during CAP exposure period. There were prominent differences be-tween CAP and filtered air exposures for all three parameters.
Table 1 shows the results of fixed effects in linear mixed-effects modeling. As shown, significantαm, for m = 1 to 6, indicated that chambering the animals into holders would sig-nificantly increase HRE and MBP and decrease QAI. These chamber effects were most prominent initially, and diminished to some extent toward the end of experiments. After the adjust-ment of chamber effects, HRE significantly increased during CAP exposures in spring season, to a maximum increase of
51.6 bpm ( p < .001) at the end of experiments. The CAP-related increase of HRE was less prominent in summer expo-sures, however. The changes of MBP caused by CAP exposure were somewhat different between the two seasons. MBP in-creased to a maximum of 8.7 mm Hg ( p= .002) at the end of spring exposures, while the changes were not significant dur-ing the summer experiments. The linear mixed-effects model-ing also demonstrated the potential for CAP to decrease the QAI through the exposure course, with a maximum decrease of 1.60 ms ( p= .001) at the end of the spring exposures, but not significant decrease in summer experiments.
In Figure 2, the averaged observed PM effects on HRE (up-per panel), MBP (middle panel), and QAI (lower panel) were plotted against clock hours (by symbols ×) with data from spring experiments showing on the left-hand column and those from summer on the right. The estimated PM effects, predicted from linear mixed-effects models (by symbols—for 11:00 to 16:00), together with 95% confidence intervals (vertical bars for 11:00 to 16:00), showed increased HRE and MBP and de-creased QAI in spring exposures. These CAP-related changes were less prominent in summer, however. The close approxi-mation between observed (×) and estimated (—) PM effects demonstrated the goodness of fit (GOF) of the mixed-effects models. The PM effects after exposures were smoothed by ro-bust locally linear fits to delineate their course returning to the baseline (solid curves after 16:00).
DISCUSSION
In this study, we demonstrated that animals exposed to CAP had increased HRE and MBP and decreased QAI in experiments conducted in the spring. However, this trend was less prominent in the summer.
Epidemiological studies have shown that increased heart rate is associated with increased ambient PM (Pope et al., 1999; Peters et al., 1999). However, the relationship between heart rate and PM has been inconsistent in animal studies, depend-ing on the experimental designs used. Decreased heart rate has been observed in animals exposed to tracheally instilled ROFA (Watkinson et al., 2001, 2003), and tracheally instilled PM (Kang et al., 2002). Furthermore, transition metals have been linked to this cardiovascular change of PM (Campen et al., 2001; Muggenburg et al., 2003). However, heart rate increase was observed in pulmonary hypertensive SD rats exposed to CAP (Gordon et al., 1998), though decreased heart rate was also observed on SH rats exposed to CAP (Nadziejko et al., 2002). Because of intersubject variability and changes of circadian cy-cles of heart rate, the results of previous studies have been in-consistent. Using repeated measurements of heart rate for each animal and a mixed-effects model analysis, we have previously demonstrated that CAP exposure could decrease HRE and MBP on SD rats with pulmonary hypertension (Cheng et al., 2003). Interestingly, we observed that CAP increased HRE on SH rats in the spring experiments, while the responses in the summer were less prominent.
TABLE 1
Regression results of fixed effects on HRE, MBP, and QAI using a linear mixed-effects model
HRE (bpm) MBP (mm Hg) QAI (ms)
Season/coefficient Value SE p Value Value SE p Value Value SE P Value
Spring α1 109.2 6.0 .000 36.0 2.7 .000 −3.76 0.24 .000 α2 100.3 6.2 .000 30.3 2.2 .000 −3.43 0.38 .000 α3 86.4 6.4 .000 29.1 2.2 .000 −3.56 0.37 .000 α4 74.7 6.8 .000 25.7 2.9 .000 −3.37 0.37 .000 α5 81.0 7.1 .000 27.3 2.2 .000 −3.73 0.37 .000 α6 64.5 8.7 .000 22.1 2.2 .000 −2.59 0.38 .000 β1 17.4 7.8 .027 2.2 2.8 .428 −0.42 0.47 .369 β2 24.0 8.8 .007 0.1 2.9 .977 −0.18 0.54 .742 β3 36.7 8.6 .000 3.1 3.6 .391 −0.69 0.51 .176 β4 45.0 8.5 .000 6.5 2.9 .025 −1.25 0.49 .011 β5 51.6 8.1 .000 8.7 2.8 .002 −1.60 0.48 .001 Summer α1 68.7 7.7 .000 33.5 2.3 .000 −2.72 0.26 .000 α2 56.7 5.0 .000 24.7 2.6 .000 −2.81 0.36 .000 α3 34.9 5.2 .000 20.0 2.4 .000 −2.23 0.50 .000 α4 13.2 5.2 .012 14.8 2.4 .000 −1.87 0.48 .000 α5 8.5 5.2 .103 13.3 2.4 .000 −2.04 0.35 .000 α6 −3.2 13.3 .810 10.1 8.3 .225 −1.15 0.33 .000 β1 23.2 11.8 .049 2.0 4.9 .680 −0.63 0.45 .159 β2 16.5 7.2 .023 −2.4 3.7 .526 −0.40 0.46 .391 β3 12.0 7.3 .104 −6.3 3.4 .061 −0.31 0.46 .498 β4 12.2 7.3 .095 −3.5 4.3 .419 −0.51 0.49 .297 β5 14.8 16.5 .371 −2.2 5.7 .696 −0.50 0.45 .265
Note. Hourly means of chambering effects were estimated by dummy variablesαm, for m = 1 to 6
corre-sponding to chamber stay from 10:00 to 16:00. Hourly means of PM effects were estimated by dummy variables
βm, for m= 1 to 5 corresponding to exposure time from 11:00 to 16:00.
With similar experimental design and analysis, different HRE responses to CAP were observed. One explanation for the discrepancy in findings may be attributable to the varia-tions in animal models. A study reported that ANS modulation over cardiovascular homeostasis was different between SD rats and SH rats (Sato et al., 2002). The hemodynamic responses to physiologic challenges were also found to be different between these two strains (McKeown & Shoukas, 1998). The other ex-planation may come from variations in exposure domain. With experiments carried out in different periods of time, we specu-lated that PM composition and concentration might be differ-ent enough to cause dissimilar action on various airway sites that were known to elicit different cardiovascular responses (Widdicombe & Lee, 2001).
Blood pressure responses to PM are less consistent and less prominent as compared to heart rate on human observations (Linn et al., 1999; Nightingale et al., 2000; Ibald-Mulli et al., 2001; Gong et al., 2003). Similarly, animal studies have been inconsistent (Toda et al., 2001; Vincent et al., 2001). In our pre-vious study (Cheng et al., 2003), MBP decreased during CAP
exposure on pulmonary hypertensive SD rats. In this research, however, we found that MBP increased with CAP in SH rats in the spring experiments, while the change was not signifi-cant in the summer. Similar explanations for heart rate may be attributable to the discrepancy in blood pressure.
Myocardium is under close modulation of ANS functioning to cope with daily and emergent incidences (Kent & Cooper, 1975; Kawano et al., 2003). Since ANS has been proposed as one of the major mechanisms linking PM and cardiac events, we speculate that cardiac contractility may be sensitive to PM exposure and can be used as an effective indicator of PM toxi-cology. Various measurements have been used in the evaluation of cardiac contractility (Tibby & Murdoch, 2003). QA inter-val (QAI), the time duration between the Q wave in the ECG and point A (the pressure upstroke) in aortograms, is sensitive in detecting changes in cardiac contractility, and independent of cardiac loading and heart rate. Owing to its simple calcu-lation and specificity to changes in cardiac contractility, QAI has been used extensively in experimental and clinical settings (Cambridge & Whiting, 1986). Recently, QAI has been used in
pharmaceutical engineering as an index of cardiac stimulation by studied substances (Alabaster et al., 1988; Bell et al., 1989; Takahara et al., 2001). However, QAI has yet to be applied in the field of inhalation toxicology.
Cardiac contractility, heart rate, and wall tension had been listed as the three determinants of myocardial oxygen demand (Ruffolo & Feuerstein, 1997). Increased cardiac contractility results in increased myocardial oxygen consumption (Cohn, 1998), and this may in turn be capable of inducing an imbal-ance between myocardial oxygen demand and supply, leading to ischemia in patients with coronary artery disease (van Rugge et al., 1992). CAP has been demonstrated in animal models to exacerbate myocardial ischemia in the face of acute occlusion of coronary arteries (Wellenius et al., 2003). In our current study, decreased QAI, or increased cardiac contractility, was noted during CAP exposures, though the responses in summer were less prominent. Thus, we postulate that QAI may be a sensitive and useful indicator in the study of PM-related cardiovascular toxicity.
The hemodynamic parameters used in the current study, in-cluding HRE, MBP, and QAI, responded less prominently in the summer observations. One explanation for this discrepancy is that CAP in the spring may have different components of PM from the summer. Further study with the characterization of CAP may shed light on the underlying mechanisms. The other explanation is a combination of aging process and hyperten-sive pathology of the SH rats. Aging has been associated with decreased cardiac contractility in both human studies (Harding et al., 1992) and animal models (Canepari et al., 1994). Molecu-lar degeneration, including diminishing cardiac muscarinic re-ceptor activity (Poller et al., 1997) and reduced sarcoplasmic calcium recycling (Kiriazis & Gibbs, 2001), makes aging hearts less responsive to either pharmacologic stimulation (Canepari et al., 1994; Ferrara et al., 1995) or physiologic challenges (Fleg et al., 1994). Alternatively, systemic hypertension has also been linked to depressed cardiac contractility and thereby to inotropic responses to pharmacologic stimuli (Ren et al., 2000). Similarly, age-related blunting of hemodynamic re-sponses, including heart rate, was also documented (Fleg et al., 1994).
Various types of receptors and neurons in mammalian air-ways have been associated with hemodynamic modulations. Rabbit upper airway and nostrils have been verified as sensitive areas linking cigarette smoke and cardiac contractility (Robleto & Peterson, 1981). Vagal pulmonary C fibers (Lai & Kou, 1998) and olfactory bulb as a whole (Moffitt et al., 2002) have been demonstrated in anesthetized SD rats as an important afferent port and integral center for cardiovascular sympathoexcitatory reflexes. We speculate that CAP might influence the hemody-namic modulations via these pathways, and thereby link to its cardiovascular pathogenesis.
The relatively small sample size of our study prevents us from drawing a firm conclusion, although the study design and powerful linear mixed-effects model did show the significance
of PM-related cardiac toxicity. Larger scale studies are still needed to verify the findings. We conclude that CAP may in-crease HRE and MBP and dein-crease QAI. The study also shows that QAI may be a sensitive and useful indicator in the study of PM-related cardiovascular toxicity.
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