Abstract
We have previously elucidated that a bell-shaped relationship exists between the central blood volume and spontaneous arterial-cardiac baroreflex function, over stepwise widespread changes in central blood volume with lower body negative pressure (LBNP) and isotonic saline infusion. However, to precisely reveal that central hypovolemia is the essential factor underlying reduced spontaneous baroreflex function in the bell-shaped relationship, it is necessary to show that not only LBNP but also plasma volume reduction can reduce spontaneous baroreflex function, as assessed by both transfer function analysis and sequence method. We therefore examined whether both spontaneous baroreflex indices of these analytical methods decrease simultaneously with central hypovolemia due to dehydration. Seven individuals were treated with 0.4 mg/kg furosemide to reduce plasma volume. We then estimated the degree of central hypovolemia and dehydration as the central venous pressure and plasma volume changed. Spontaneous baroreflex function was assessed before (Baseline) and approximately 1 hour after furosemide administration (Dehydration). Both central venous pressure (about 4 mmHg) and plasma volume (about 10%) decreased after furosemide administration. Both spontaneous baroreflex indices of high-frequency transfer function gain (Baseline 21.5 ± 3.2; Dehydration 14.9 ± 2.9 ms/mmHg) and of the sequence slope (Baseline 18.5 ± 2.8; Dehydration 14.3 ± 2.7 ms/mmHg) were significantly reduced by plasma volume reduction, similar to our previous findings during LBNP without plasma volume reduction. Thus, the results of transfer function analysis and the sequence method together suggest that central hypovolemia due to dehydration would reduce spontaneous arterial-cardiac baroreflex function via mechanisms similar to LBNP.
