Cardiovascular response to graded lower body negative pressure in young and elderly man

Lower body negative pressure (LBNP) reduces central venous pressure (CVP) a nd cardiac output. The elderly are reported to have a limited capacity to i ncrease cardiac output by increasing heart rate (HR), are especially depend ent on end diastolic volume to maintain stroke volume and therefore should be especially vulnerable to LBNP. The present study compared the effects of LBNP in the young and old. Stroke volume was assessed non-invasively as st roke distance (SD) by aortovelography. Two groups of healthy male volunteer s were studied: eight young (29.7 +/-2.0 years, mean +/- S.E.M.) and nine o ld (70.1 +/-0.9 years). LBNP was applied progressively at 17.5, 35 and 50 m mHg in 20 min steps, with measurements taken during each steady state. Ther e were similar, significant, falls in CVP in both groups. SD fell significa ntly in both groups from respective control values of 24.8 +/-1.6 and 16.6 +/-0.9 cm to 12.5 +/-1.3 and 8.9 +/-0.4 cm at a LBNP of 50 mmHg. Although S D in the elderly was significantly lower than in the young, the LBNP-induce d changes were not different between groups. Both groups produced similar s ignificant increases in vascular resistance, HR, plasma vasopressin (AVP) a nd noradrenaline. Mean arterial blood pressure (MBP) and plasma adrenaline did not change significantly. Therefore healthy old men respond to LBNP in a similar manner to the young, although MBP and SD are regulated around dif ferent baselines in the two groups.