Clinical science
-
Clinical Trial Controlled Clinical Trial
Impact of changes in respiratory frequency and posture on power spectral analysis of heart rate and systolic blood pressure variability in normal subjects and patients with heart failure.
1. Autonomic dysfunction is a major feature of congestive cardiac failure and may have an important role in determining progression and prognosis. The low-frequency/high-frequency ratio derived from power spectral analysis of heart rate variability has been proposed as a non-invasive method to assess sympatho-vagal balance. ⋯ Systolic blood pressure low- and high-frequency components and their ratio were significantly affected by respiration (P < 0.03) and change in posture (P < 0.03) in both patients with heart failure and normal subjects, with a significant increase in the low-frequency/high-frequency ratio (P = 0.03) on standing in patients with heart failure, indicating that autonomic modulation of blood pressure is still operating in heart failure. 6. Thus, respiratory rate and changes in posture have a significant effect on measurements derived from spectral analysis of heart rate and blood pressure variability. Studies that use power spectral analysis as a measure of sympatho-vagal balance should control for these variables.
-
1. Evidence of an adrenergic component of cutaneous hyperalgesia has recently been obtained in animal models of painful peripheral neuropathy. These findings have prompted speculation that an increased density or sensitivity of peripheral alpha-adrenoceptors contributes to sensory abnormalities and chronic neuropathic pain in conditions such as reflex sympathetic dystrophy. ⋯ The mean density of alpha 1-adrenoceptors in the pain-free skin of patients (26.9 grains/1000 microns2) fell midway between receptor density in hyperalgesic skin and in the skin of normal individuals, and did not differ significantly from either. 5. Our findings indicate that alpha 1-adrenoceptors are present in the epidermis, and suggest that their numbers may be increased in the hyperalgesic skin of patients with reflex sympathetic dystrophy. Further studies need to identify the dermal and epidermal cell types that express high densities of alpha 1-adrenoceptors, and to investigate their normal function and role in neuropathic pain.
-
1. The non-invasive method of near-infrared spectroscopy was used to measure myocardial oxygenation and haemodynamics in response to left anterior descending coronary artery occlusion in a porcine model. 2. Near-infrared spectroscopy measures changes in haemoglobin (and myoglobin) oxygenation and blood volume to yield information on tissue perfusion and flow. ⋯ Moreover, the time for the deoxyhaemoglobin signal to reach maximum values was found to correlate with the duration of occlusion (P < 0.04). This could be indicative of the PO2 of the ischaemic tissues and an immediate off-loading of oxygen from oxyhaemoglobin. The results are reliable, reproducible and sensitive enough to detect the kinetics of haemoglobin oxygenation from a beating heart in situ.