Spectral analysis of cooling induced hemodynamic perturbations indicates involvement of sympathetic activation and nitric oxide production in rats.

AIMS: Oscillations in arterial pressure and heart period in response to cold stress are poorly understood. We used a telemetric device with spectral and cross-spectral analyses to assess variabilities in the heart rate (HRV) and blood pressure (BPV) of conscious rats receiving a cooling stimulus (CS) (rapid immersion of palms and soles into 4°C water) at ambient thermoneutral conditions (TC), in a cold room (CC), and when under pentobarbital anesthesia (UA).

MAIN METHODS: Power spectra of very low, low, and high frequencies (VLF: 0.02 to 0.2Hz, LF: 0.2 to 0.6Hz, and HF: 0.6 to 3.0Hz), dicrotic notch (Dn) and plasma nitric oxide (NO) levels were measured for statistical comparisons.

KEY FINDINGS: When compared to resting rats (PreCS), CS evoked in rats the following hemodynamic perturbations: 1) pressor and tachycardia; 2) increases in VLFBPV, LFBPV, HFBPV, and TPBPV but decreases in VLFHRV, LFHRV, and TPHRV; 3) a positive correlation between LFBPV and VLFBPV but an inverse correlation between VLFHRV and VLFBPV and LFHRV and LFBPV; 4) high coherence value at frequency region of LF between BPV and HRV; and 5) increase of NO production and disappearance of Dn. Additionally, CS of CC and UA rats compared with TC rats evoked different patterns of hemodynamic perturbations; CC rats were activated but UA rats were inactivated.

SIGNIFICANCE: Our findings indicate that changes in VLFBPV are related to the myogenic vascular responsiveness to CS. Power spectra changes to CS are highly relevant to sympathetic activation and NO production.