A comparison of pharmacologic and spontaneous baroreflex methods in aging and hypertension.
BACKGROUND
Phenylephrine bolus injection is an established technique to measure baroreflex sensitivity (BRS). This study quantified the relationship between the phenylephrine method and noninvasive measures of BRS and examined the effects of aging and hypertension on BRS. We also examined whether heart rate variability (HRV) provides as much information as does BRS.


METHODS
BRS was determined by phenylephrine bolus (BRSphe), amyl nitrite inhalation (BRSamyl), Valsalva maneuver (BRSVals) and by time (BRS(+)) and spectral domain analysis (BRS(LFalpha), 004-015 Hz) of spontaneous blood pressure and R-R interval changes over the 5-min time period.


RESULTS
The phenylephrine method significantly correlated with other methods (BRS(LFalpha) R = 0.54, BRS(+) R = 0.55, BRSVals R = 0.43 and BRSamyl R = 0.39; P < or = 0.001). Each method underestimated the BRSphe by the factors 0.62, 0.64, 0.59 and 0.33, respectively; P value less than 0.001. Only BRS(LFalpha) was significantly different between normotensive and hypertensive patients in young [24.3 +/- 1.4 (n = 40) vs. 12.2 +/- 2.3 (n = 7)] and middle-aged [16.5 +/- 1.1 (n = 71) vs. 10.8 +/- 1.1 (n = 31) groups, respectively]. HRV in the high frequency band (0.15-0.40 Hz) was significantly lower in young hypertensive patients than in normal controls (26 +/- 6.0 vs. 50 +/- 2.4, P < 0.05).


CONCLUSIONS
Although all methods correlated with the phenylephrine technique, none of them could be used interchangeably with that technique. BRS(LFalpha) detected the baroreflex loss of hypertension most clearly, and BRSamyl did not differ among groups.
Department of Medicine, University of California at San Diego, San Diego, California 92103-8341, USA.
Milos
M
Milic
Ping
P
Sun
Fujun
F
Liu
Claudia
C
Fainman
Joel
J
Dimsdale
Paul J
PJ
Mills
Michael G
MG
Ziegler
D000280:Administration, Inhalation; D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000680:Amyl Nitrite / Q000008:administration & dosage; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology*; D016022:Case-Control Studies; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D010656:Phenylephrine / Q000008:administration & dosage; D014636:Valsalva Maneuver / Q000502:physiology; D055815:Young Adult
D010656:Phenylephrine; D000680:Amyl Nitrite