Abstract
A double-blind paired protocol was used to evaluate, in eight male volunteers, the effects of the endogenous opiate antagonist naloxone (NAL; 0.05 mg· kg−1) on cardiovascular responses to 50° head-up tilt-induced central hypovolaemia. Progressive central hypovolaemia was characterized by a phase of normotensive-tachycardia followed by an episode of hypotensive-bradycardia. The NAL shortened the former from 20 (8–40) to 5 (3–10) min (median and range; (P < 0.02). Control head-up tilt increased the means of thoracic electrical impedance [from 35.8 (SEM 2.1) to 40.0 (SEM 1.8) Ω; P < 0.01 of heart rate [HR; from 67 (SEM 5) to 96 (SEM 8) beats · min−1, P < 0.02], of total peripheral resistance [TPR; from 25.5 (SEM 3.2) to 50.4 (SEM 10.5)mmHg min 1−1, P < 0.05] and of mean arterial pressure [MAP; from 96 (SEM 2) to 101 (SEM 2)mmHg, P < 0.02]. Decreases were observed in stroke volume [from 65 (SEM 12) to 38 (SEM 9) ml, P < 0.01], in cardiac output [from 3.7 (SEM 0.7) to 2.5 (SEM 0.5) 1 · mint, P < 0.01], in pulse pressure [from 55 (SEM 4) to 37 (SEM 3)mmHg, P < 0.01] and in central venous oxygen saturation [from 73 (SEM 2) to 59 (SEM 4)%, P < 0.01]. During NAL, mean HR increased from 70 (SEM 3); n.s. compared to control) to only 86 (SEM 9) beats · min−1 (P < 0.02 compared to control) and MAP remained stable. The episode of hypotensive-bradycardia appeared as mean control HR decreased to 77 (SEM 7)beats · min−1, TPR to 31.4(SEM 7.7)mmHg · min · 1−1 and MAP to 60 (SEM 5)mmHg (P < 0.01), and the volunteers were tilted supine. Cardiovascular effects of naloxone on central hypovolaemia included a reduced elevation of HR and blood pressures and provocation of the episode of hypotensive-bradycardia.
Original language | English |
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Journal | European Journal of Applied Physiology and Occupational Physiology |
Volume | 70 |
Issue number | 3 |
Pages (from-to) | 246-251 |
Number of pages | 6 |
ISSN | 0301-5548 |
DOIs | |
Publication status | Published - Mar 1995 |
Keywords
- Bradycardia
- Central venous pressure
- Endogenous opioids
- Hypovolaemia
- Tachycardia