Pulmonary Exposure to Multi‑Walled Carbon Nanotubes Elevates Blood Pressure and Impairs Cardiac Function in Rats

Abstract

Background

Heart rate variability (HRV) is a sensitive marker of autonomic nervous system (ANS) balance and predicts cardiovascular outcomes. Prior work from our laboratory demonstrated that inhalation of multi‑walled carbon nanotubes (MWCNTs) in rats augments both sympathetic and parasympathetic tone, implying that engineered nanoparticles (ENs) can modify cardiovascular function. The present study extends these observations by recording real‑time blood pressure, heart rate, and cardiac performance following MWCNT inhalation, and by linking these changes to HRV alterations.

Methods

Male Sprague‑Dawley rats (275–300 g) were surgically implanted with a telemetry transmitter (HD‑S21, Data Sciences International) and exposed to a 5 mg/m³ aerosol of MWCNTs for 5 h. Continuous electrocardiogram (EKG) and blood pressure data were collected before, during, and at 1 and 7 days after exposure. Cardiac function was assessed in anesthetized rats using a pressure‑volume (PV) loop catheter (Millar SPR‑901) and graded dobutamine infusion (1.25–10 μg/kg).

Results

Inhalation of MWCNTs produced a rapid, dose‑dependent rise in systolic, diastolic, and mean arterial pressure (MAP) that persisted for the 5‑h exposure period (p < 0.01) and remained modestly elevated at 1 day post‑exposure (p < 0.05). Heart rate fell during exposure, trending toward significance (p = 0.054). In anesthetized rats, MWCNT exposure slightly depressed basal stroke volume (SV), stroke work (SW), and cardiac output (CO), and markedly reduced the dobutamine‑induced augmentation of SV, SW, and CO at 1 day post‑exposure (p < 0.01). No significant differences were observed at 7 days post‑exposure. Blood pressure responses to dobutamine were unchanged between groups.

Conclusions

Pulmonary exposure to MWCNTs transiently elevates blood pressure and dampens cardiac responsiveness in rats, likely through simultaneous activation of sympathetic and parasympathetic pathways that alter ANS balance. These findings underscore the need to investigate whether such autonomic perturbations can precipitate cardiovascular events in susceptible populations.

Background

With increasing industrial use of nanomaterials, occupational exposure is rising, and animal studies have linked short‑term pulmonary exposure to engineered nanoparticles (ENs) with lung inflammation, fibrosis, and carcinogenesis. Emerging evidence indicates that ENs also affect cardiovascular health via inflammation, translocation, or neural mechanisms. Our own investigations showed that low‑dose exposure to ultrafine titanium dioxide (UFTiO₂) and MWCNTs modestly inflames the lung yet triggers transient increases in peripheral neurotransmitter synthesis and HRV changes, suggesting neuronal mediation rather than direct cardiac contact.

The ANS maintains cardiovascular homeostasis; disturbances can lead to hypertension, arrhythmias, or stroke. Epidemiological data demonstrate that even brief inhalation of particulate air pollution, especially ultrafine particles, raises cardiovascular morbidity by shifting ANS balance. Because nano‑sized particles penetrate deep into the alveoli and bypass mucociliary clearance, they can stimulate pulmonary sensory neurons continuously, potentially altering central autonomic control.

Methods

Animal Preparation

Male Sprague‑Dawley rats were acclimated for one week, housed in specific pathogen‑free conditions, and monitored for health. All procedures were approved by the NIOSH Animal Care Committee.

MWCNT Exposure

Rats were exposed individually in sealed cages connected to a main aerosol chamber via anti‑static tubing. A 5 mg/m³ MWCNT aerosol (5 μm mass median aerodynamic diameter) was generated and characterized by cascade impactor and gravimetric analysis. Estimated lung burden per rat was ~5–7 μg, comparable to occupational exposures.

Telemetry Implantation

Under isoflurane anesthesia, the abdominal aorta was cannulated with a telemetry catheter and the device secured beneath the abdominal wall. Post‑operative analgesia was provided, and animals were allowed a 3‑week recovery before exposure.

Hemodynamic Measurements

In anesthetized rats, a Millar PV loop catheter was advanced through the carotid artery into the left ventricle. Baseline recordings were stabilized for 20 min before dobutamine infusion at incremental doses (1.25–10 μg/kg). Signals were sampled at 1 kHz and analyzed with the MPVS‑Ultra system.

Data Acquisition and Analysis

Blood pressure was recorded continuously for 24 h pre‑exposure, during the 5‑h exposure, and at 1 and 7 days post‑exposure. Data were exported to Excel and analyzed by repeated‑measures ANOVA with Fisher’s LSD; p < 0.05 was considered significant.

Results

Figure 1 illustrates the aerosol size distribution (mass median aerodynamic diameter 1.4 μm). During exposure, systolic, diastolic, and mean arterial pressures increased significantly relative to filtered‑air controls (Figure 2). At 1 day post‑exposure, pressure elevations persisted but were not statistically significant; by 7 days, pressures returned to baseline.

Cardiac PV loop analysis (Figures 3–5) revealed that MWCNT exposure slightly lowered basal SV, SW, and CO and markedly attenuated the dobutamine‑induced rise in these parameters at 1 day post‑exposure. No differences were seen at 7 days. Mean blood pressure responses to dobutamine were unchanged (Figure 6).

Discussion

Our findings confirm that pulmonary MWCNT exposure elevates blood pressure in freely moving rats, likely through sympathetic activation. Concurrently, heart rate falls and cardiac responsiveness to β‑adrenergic stimulation is blunted, consistent with enhanced parasympathetic tone. The simultaneous increase in both sympathetic and parasympathetic activity suggests a complex ANS modulation rather than a simple baroreflex response.

Possible mechanisms include direct stimulation of central autonomic nuclei by inhaled particles or peripheral neuronal activation bypassing the baroreceptor reflex. Importantly, these autonomic shifts occur rapidly and resolve within days, yet may represent a trigger for cardiovascular events in susceptible individuals.

Conclusions

Inhalation of MWCNTs induces transient autonomic changes that elevate blood pressure and impair cardiac function in rats. Further research is warranted to determine whether these effects exacerbate cardiovascular risk in populations with pre‑existing disease.

Abbreviations

CNTS

Carbon nanotubes

CO

Cardiac output

DBP

Diastolic blood pressure

EKG

Electrocardiogram

ENs

Engineered nanoparticles

HR

Heart rate

HRV

Heart rate variability

MAP

Mean blood pressure

MWCNTs

Multi‑walled carbon nanotubes

SBP

Systolic blood pressure

SV

Stroke volume

SW

Stroke work