A decrease in heat-induced cutaneous vasodilatation has been implicated as the cause of increased heat stress in the elderly. We used laser Doppler techniques to study the skin blood flow response to local heat in 82 healthy volunteers. There were 39 young volunteers, mean age 29 +/- 1, and 43 elderly volunteers, mean age 76 +/- 1. There was minimal difference in skin blood flow at 35 degrees C between the two groups. In contrast, skin blood flow at 44 degrees C was significantly lower in the older subjects at nutritively perfused sites, such as the knee and elbow. However, there was no difference between the young and old groups in skin blood flow at the finger or toe pulp, sites with primarily arteriovenous anastomotic (AVA) flow. In the older subjects, the two components of skin blood flow, microvascular volume (VOL) and red blood cell velocity (VEL), were both decreased at 44 degrees C at nutritive sites, but not at AVA sites. Regression analysis demonstrated a linear fall in blood flow, VOL, and VEL with advancing age at nutritive sites at 44 degrees C. We conclude that thermally-induced cutaneous blood flow is reduced in older persons at nutritive capillary sites, but not at AVA sites.
Increasing the total surface area of the pulmonary blood-gas interface by capillary recruitment is an important factor in maintaining adequate oxygenation when metabolic demands increase. Capillaries are known to be recruited during conditions that raise pulmonary blood flow and pressure. To determine whether pulmonary arterioles and venules are part of the recruitment process, we made in vivo microscopic observations of the subpleural microcirculation (all vessels less than 100 microns) in the upper lung where blood flow is low (zone 2). To evoke recruitment, pulmonary arterial pressure was elevated either by an intravascular fluid load or by airway hypoxia. Of 209 arteriolar segments compared during low and high pulmonary arterial pressures, none recruited or derecruited. Elevated arterial pressure, however, did increase the number of perfused capillary segments by 96% with hypoxia and 165% with fluid load. Recruitment was essentially absent in venules (4 cases of recruitment in 289 segments as pressure was raised). These data support the concept that recruitment in the pulmonary circulation is exclusively a capillary event.
We studied 40 healthy elderly and 31 healthy young volunteers and 25 elderly diabetic and 37 young diabetic patients. All subjects received detailed neurological examinations focusing particularly on sensory symptom and physical evaluations. Standardized assessment of symptoms and physical testing of light touch, pain, vibratory and thermal sensation were performed at the hand, wrist, elbow, foot, ankle and knee. The total symptom score (SS) and the total physical score (PS) were defined by summing test scores at each site. Current perception threshold (CPT) testing using constant current sine wave alternating current was completed at the same anatomical sites. CPT findings did not differ significantly between young and old healthy subjects. Older diabetic patients had higher CPTs than younger diabetic patients, but the severity of clinical diabetic neuropathy was greater in the older group. CPTs correlated with the degree of clinical diabetic neuropathy (r = 0.47 with SS and r = 0.60 with PS) rather than with age (r = 0.12). We conclude that current perception does not decline with age. Nor does ageing by itself worsen CPT values in patients with neuropathy. CPT testing is easily performed, clinically applicable and the first objective sensory measure not affected by the process of ageing.
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