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Reduced cardiopulmonary baroreflex sensitivity in patients with hypertrophic cardiomyopathy
H L Thomson1, J Morris-Thurgood, J Atherton
1Department of Medicine, University of Queensland.
Insights
Patients with hypertrophic cardiomyopathy (HCM) show impaired baroreflex function, specifically a defect in the afferent limb of the cardiopulmonary reflex arc. This finding is crucial for understanding cardiovascular autonomic control in HCM.
Area of Science:
- Cardiology
- Autonomic Neuroscience
- Cardiovascular Physiology
Background:
- Previous research identified cardiopulmonary baroreflex abnormalities in vasovagal syncope.
- Hypertrophic cardiomyopathy (HCM) patients exhibit altered vascular control during exercise and tilt.
- A hypothesis posited similar afferent cardiopulmonary baroreflex defects in HCM.
Purpose of the Study:
- To evaluate baroreflex function in individuals diagnosed with hypertrophic cardiomyopathy (HCM).
Main Methods:
- Assessed baroreceptor sensitivity using phenylephrine and lower body negative pressure (LBNP) in 29 HCM patients and 32 controls.
- Measured forearm vascular resistance (FVR) during LBNP to assess cardiopulmonary baroreceptor sensitivity.
- Evaluated carotid artery baroreflex sensitivity and efferent limb integrity through various physiological tests.
Main Results:
- HCM patients demonstrated a significantly blunted forearm vascular resistance (FVR) response to LBNP compared to controls (2.36±9 U vs. 123±8.76 U, p=0.001).
- A paradoxical fall in FVR occurred in 8 HCM patients, unlike any control subjects.
- Patients with a history of syncope showed a further decrease in FVR during LBNP compared to those without syncope (p=0.014).
Conclusions:
- The study indicates a defect in the afferent limb of the cardiopulmonary reflex arc in patients with hypertrophic cardiomyopathy (HCM).
- This dysfunction may contribute to the observed autonomic dysregulation in HCM patients.
Objectives:
We sought to assess baroreflex function in patients with hypertrophic cardiomyopathy (HCM).
Background:
We have previously demonstrated a specific abnormality in the afferent limb of the cardiopulmonary baroreflex in patients with vasovagal syncope. Patients with HCM exhibit abnormal control of their vasculature during exercise and upright tilt; we therefore hypothesize a similar abnormality in the afferent limb of the cardiopulmonary baroreflex arc.
Methods:
We investigated 29 patients with HCM and 32 control subjects. Integrated baroreceptor sensitivity was assessed after administration of phenylephrine. Cardiopulmonary baroreceptor sensitivity was assessed by measuring forearm vascular resistance (FVR) during lower body negative pressure (LBNP). Carotid artery baroreflex sensitivity was assessed by measuring the in RR interval during manipulation of carotid artery transmural pressure. The integrity of the efferent limb of the reflex arc was determined by studying responses to both handgrip and peripheral alpha-receptor sensitivity.
Results:
During LBNP, FVR increased by only 2.36+/-9 U in patients, compared with an increase of 123+/-8.76 U in control subjects (p=0.001). FVR paradoxically fell in eight patients, but in none of the control subjects. Furthermore, FVR fell by 4.9+/-5.6 U in patients with a history of syncope, compared with an increase of 4.7+/-7.2 U in those without syncope (p=0.014). Integrated and carotid artery baroreflex sensitivities were similar in patients and control subjects (14+/-7 vs. 14+/-6 ms/mm Hg, p=NS and -3+/-2 vs. -4+/-2 ms/mm Hg, p=NS, respectively). Similarly, handgrip responses and the dose/response ratio to phenylephrine were not significantly different.
Conclusions:
This study suggests that patients with HCM have a defect in the afferent limb of the cardiopulmonary reflex arc.