Hemodynamic and hormonal changes during lower body negative pressure in bedridden disabled patients

Abstract

Hemodynamic responses and hormonal changes induced by lower body negative pressure (LBNP) were measured in bedridden patients with severe disabilities to identify their cardiovascular function. After a control period of 5 minutes supine, each subject underwent a LBNP test of ‐20 mmHg for 5 minutes. Disabled patients were classified into two groups: Group HI consisted of the members who had a blood pressure response to LBNP exposure similar to normal control subjects, and group H2 patients displayed a greater reduction in blood pressure than the normal response. Both disabled groups demonstrated a significantly higher level of resting heart rate as well as a smaller stroke volume and cardiac output than normal subjects. Exposure to LBNP in disabled patients produced a smaller decrement in stroke volume and cardiac output than in normal subjects. The expected increase in heart rate for the compensatory effect was not observed in the HI group, and a decreased heart rate lower than resting values was measured in the H2 group. The norepinephrine response of the disabled groups was found to be insufficient compared with normal subjects. It is suggested that cardiovascular deconditioning of disabled patients is caused not only by a decrease in total blood volume, but also by impairment of baroreflex activity both centrally and peripherally due to the patient's extremely prolonged recumbency.