Hypertension-related hypoalgesia, autonomic function and spontaneous baroreflex sensitivity.
OBJECTIVE
The mechanisms involved in the relationship between pain perception and hypertension are poorly understood. This study has sought to investigate whether the spontaneous baroreflex sensitivity and the autonomic nervous system balance are related to hypertension-associated hypoalgesia.


METHODS
In the morning, 73 untreated male subjects (45 hypertensives, 28 normotensives) were submitted to a simultaneous recording of electrocardiographic and blood pressure signals in resting condition. The tracings were analysed off-line to evaluate the spectral components of the low frequency (LF) and high frequency (HF) powers (autoregressive algorithm; LF/HF ratio used in subsequent analysis as an index of sympathovagal balance), and the alphaLF (alphaLF), an index of baroreflex sensitivity. After the rest period, the subjects underwent dental pain perception evaluation (pulpar tester: test current increasing from 0 to 0.03 mA, expressed in relative Units) to determine the dental pain threshold and tolerance. Afterwards, a 24-h ambulatory blood pressure monitoring was performed.


RESULTS
A significant relationship was observed between alphaLF and pain threshold (r = -0.34; p = 0.003). When a multivariate analysis was computed to control for age, 24-h systolic pressure and LF/HF ratio, alphaLF was a predictive independent factor associated with pain threshold (model p = 0.019; r = -0.31; p = 0.025). Moreover, the 24-h systolic pressure was independently associated with pain threshold (model p = 0.019; r = 0.30, p = 0.031). The relationship between alphaLF and relative tolerance was not statistically significant. When the association between the LF/HF ratio and pain sensitivity was assessed as a secondary endpoint, no significant relationship was observed. Since no significant interaction was found, the effect of alphaLF and LF/HF ratio on pain perception was assumed to be similar in normotensive and hypertensive subjects.


CONCLUSIONS
The relationship found between unstimulated baroreflex sensitivity and pain threshold suggests a modulation of pain perception by baroreflex pathways in hypertension-associated hypoalgesia. In a baseline condition, the autonomic nervous system balance does not seem to influence pain sensitivity.
Guasti
Luigina
L
Department of Clinical and Biological Sciences, University of Insubria, Ospedale di Circolo, Varese, Italy. luigina.guasti@uninsubria.it
Zanotta
Danilo
D
Mainardi
Luca T
LT
Petrozzino
Maria R
MR
Grimoldi
Paola
P
Garganico
Deborah
D
Diolisi
Alessio
A
Gaudio
Giovanni
G
Klersy
Catherine
C
Grandi
Anna M
AM
Simoni
Cinzia
C
Cerutti
Sergio
S
D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017288:Pain Threshold; D012016:Reference Values; D013599:Systole