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Cardiopulmonary responses to exercise in patients with hypertrophic cardiomyopathy
S Jones1, P M Elliott, S Sharma
1Department of Physiology, St George's Hospital Medical School, London, UK.
Insights
Patients with hypertrophic cardiomyopathy show significantly reduced exercise capacity, including peak oxygen uptake and anaerobic threshold. These findings highlight severe abnormalities in gas exchange, impacting overall exercise tolerance.
Area of Science:
- Cardiology
- Exercise Physiology
- Pulmonary Medicine
Background:
- Hypertrophic cardiomyopathy (HCM) is a genetic heart condition characterized by thickening of the heart muscle.
- Exercise intolerance is a common symptom in HCM patients, but the underlying physiological mechanisms require further elucidation.
Purpose of the Study:
- To investigate the submaximal and maximal exercise response in patients diagnosed with hypertrophic cardiomyopathy.
- To identify abnormalities in cardiopulmonary gas exchange during exercise in HCM patients.
Main Methods:
- A prospective study involving 50 patients with HCM and 22 healthy sedentary controls undergoing incremental cycle ergometry.
- Continuous monitoring of respiratory gases and ECG to assess variables like peak oxygen uptake (VO2 peak) and anaerobic threshold.
Main Results:
- HCM patients exhibited significantly reduced VO2 peak and anaerobic threshold compared to controls (p < 0.0001).
- A majority of HCM patients (59%) had VO2 peak <60% of predicted values, and 50% had anaerobic threshold <60% of predicted.
- Abnormalities in oxygen uptake/work rate relation and maximum oxygen pulse were observed, with increased ventilation/carbon dioxide output slope in 72% of patients.
Conclusions:
- Severe abnormalities in maximal and submaximal exercise indices were found in HCM patients.
- Reduced stroke volume, ventilation/perfusion mismatch, and impaired peripheral oxygen utilization are suggested mechanisms for exercise intolerance in HCM.
Objective:
To examine the submaximal and maximal indices of the exercise response of patients with hypertrophic cardiomyopathy.
Design And Setting:
Prospective examination of cardiopulmonary responses to ramp exercise test of a consecutive group of patients with hypertrophic cardiomyopathy attending a cardiomyopathy outpatient clinic.
Methods:
50 patients aged 12 to 76 years (mean (SD) 35 (14)) with diagnosis of hypertrophic cardiomyopathy performed incremental cycle ergometry; 22 sedentary volunteers (seven female, 15 male) aged 14 to 58 years (mean (SD) 31 (12)) served as controls. Respiratory gas was continuously sampled from the mouth-piece, and its concentration profile phase aligned to the respired air flow signals. Following analogue to digital conversion, gas exchange variables were computed breath by breath and the data were averaged every 30 seconds for graphic display. A 12 lead ECG was monitored continuously and recorded every three minutes during the exercise.
Results:
Both the peak oxygen uptake attained on the test (VO2 peak) and anaerobic threshold were reduced in patients with hypertrophic cardiomyopathy compared with the control group (p < 0.0001). In 29 patients (59%) the VO2 peak was less than 60% and only two patients achieved a peak above 80% of their predicted values. The anaerobic threshold was below 60% of the predicted value in 31 patients and above 80% in only three patients. The slope of oxygen uptake/work rate relation (delta VO2/delta WR) was decreased in 16 patients (32%). The maximum oxygen pulse (VO2/HR) was reduced as a percentage of the predicted value, and became flat at high work rates in 32 patients. There was a significant correlation between anaerobic threshold and VO2 peak (p < 0.0001), work efficiency (p < 0.0001), and maximum oxygen pulse (p < 0.0001). The slope of change in ventilation against change in carbon dioxide output (delta VE/delta VCO2) for the subanaerobic threshold range was increased in 36 patients (72%) and was inversely correlated with anaerobic threshold (p < 0.0002).
Conclusions:
There were severe abnormalities in maximal and submaximal indices of pulmonary gas exchange in a cohort of hypertrophic cardiomyopathy patients attending a referral cardiovascular clinic. The pattern of the abnormalities suggests that a reduced stroke volume response, ventilation/perfusion mismatch, and abnormal peripheral oxygen utilisation are the possible mechanisms of exercise intolerance.