Non-respiratory components of heart rate variability in heart transplant recipients: evidence of autonomic reinnervation?
1. Although the high-frequency fluctuations in R-R interval (respiratory sinus arrhythmia) observed in heart transplant recipients are not a reliable marker of reinnervation because of a previously shown direct mechanical effect of breathing, the presence of a non-respiration-related low-frequency oscillation reflects rhythms generated outside the heart, and thus could be neurally mediated. 2. To evaluate the presence of reinnervation, the spontaneous variability in R-R interval was investigated, supine and after passive tilting, in 23 heart transplant recipients (age 43 years, range 23-64 years) and in 25 normotensive control subjects by autoregressive spectral analysis of low- and high-frequency spontaneous fluctuations in R-R interval and respiration. The response of R-R interval to amyl nitrite inhalation was also evaluated in five heart transplant recipients and eight control subjects. 3. Detectable low-frequency oscillations, unrelated to respiration, were present in 13/23 heart transplant recipients, particularly in those who were transplanted at least 20 months earlier (11/14). The natural logarithm of the power of low-frequency fluctuations was markedly lower than in control subjects (0.75 +/- 0.21 versus 5.62 +/- 0.20 ms2, P < 0.001). The low-frequency but not the high-frequency fluctuations correlated with time since transplantation (r = 0.44, P < 0.05). The subjects with low-frequency fluctuations showed a sudden decrease in R-R interval with amyl nitrite linearly related to the decrease in mean blood pressure (r > or = 0.94). The slopes obtained in these heart transplant recipients were comparable (although of lower values) with those obtained in control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Bernardi
L
L
Dipartimento di Medicina Interna, Sezione Clinica Medica I, Pavia, Italy.
Valle
F
F
Leuzzi
S
S
Rinaldi
M
M
Marchesi
E
E
Falcone
C
C
Martinelli
L
L
Viganó
M
M
Finardi
G
G
Radaelli
A
A
D000328:Adult; D000680:Amyl Nitrite / Q000494:pharmacology; D001341:Autonomic Nervous System / Q000502:physiology*; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D016027:Heart Transplantation / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D011184:Postoperative Period; D011187:Posture / Q000502:physiology; D012119:Respiration / Q000502:physiology; D013268:Stimulation, Chemical
D000680:Amyl Nitrite