Blood flow cessation at external pressure in the skin of normal human limbs. Photoelectric recordings compared to isotope washout and to local intraarterial blood pressure.
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Biomedical subjects
Publications and source records attributed to P Holstein.
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This paper is devoted to elucidation of the question: Which external pressure is required to stop skin blood flow at the skin - support interface in humans lying on the back in the supine position? Cessation of blood flow was recorded as cessation of washout of an intracutaneous depot of 131I-antipyrine mixed with histamine. The external pressure was measured by a small airfilled plastic cushion connected to a mercury manometer. In 11 normal subjects, eight patients with hypertension and seven patients with tetra- or paraplegia the "flow cessation external pressure" (FCEP) was strongly correlated to the auscultatory brachial mean blood pressure (p less than or equal to 0.001). The difference mean blood pressure - FCEP was on average 4 mmHg (range (-11) - (+20) mmHg) and there was no significant difference between the three groups studied. Thus external pressure exceeding the actual mean blood pressure will stop skin circulation.
In 60 below-knee amputations the healing of the stumps was correlated with the local skin perfusion pressure (SPP) measured preoperatively as the external pressure required to stop isotope washout using 131I- or 125I--antipyrine mixed with histamine. Of the eight cases with an SPP below 20 mmHg, no less than six (75 per cent) failed to heal and required reamputation at the above-knee level. Of the 12 cases with an SPP between 20 and 30 mmHg four cases (33 per cent) failed to heal but of the 40 cases with an SPP above 30 mmHg, there were only four cases (10 per cent) which did not heal. The difference in failure rate is highly significant (P less than 0.01). Four out of 30 diabetic patients required reamputation as against 10 out of 30 non-diabetics (0.05 less than P less than 0.10). The average SPP was higher in the diabetic group: 57 mmHg (range 18-93 mmHg) compared with 34 mmHg (range 8-68 mmHg) in the non-diabetic group (P less than 0.001). The postoperative SPP measured on the stumps was on average 8 mmHg higher than the preoperative SPP (P less than 0.001). The increase took place mainly in stumps with an SPP above 20 mmHg explaining why the preoperative SPP values related so closely to the postoperative clinical course. We conclude that a low SPP can be used to predict ischaemic wound complications, leading to reamputation at a higher level.
In 59 above-knee amputations healing of the stumps was correlated with the local skin perfusion pressure (SPP) measured preoperatively as the external pressure required to stop isotope washout using 1318-- or 125I--antipyrine mixed with histamine. Out of the 11 cases with an SPP below 30 mmHg no less than nine (82 per cent) suffered severe wound complications. Out of the 48 cases with an SPP above 30 mmHg severe wound complications occurred in only four cases (8 per cent). The difference in wound complication rate is highly significant (P less than 0.01). The postoperative SPP measured on the stumps was on average only slightly and insignificantly higher than the preoperative values, explaining why the preoperative values related so closely to the postoperative clinical course. We conclude that the SPP can be used to predict ischaemic wound complications in above-knee amputations as has previously been shown to be the case in below-knee amputations.
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The skin perfusion pressure was measured as the external pressure required to stop blood flow, as evidenced by cessation of the washout of an intracutaneous depot of [131I-]antipyrine mixed with histamine. The external pressure on the skin was measured by an 11 x 11 cm slack air-filled plastic cushion connected to a mercury manometer and interposed between the labelled area and a blood pressure cuff. The 'flow cessation external pressure' (FCEP) varied parallel to the intra-arterial femoral mean blood pressure, but was on the average 10.8 mmHg (SD 6.4) lower. FCEP was measured on twenty normal subjects at four different segments of the leg. The average differences between auscultatory brachial mean blood pressure and FCEP were: thigh 12.0 mmHg (SD 7.6); calf 10.4 mmHg (SD 7.4); ankle 12.9 mmHG (SD 10.1); foot 20.2 mmHg (SD 12.1). The SD of the difference between measurements on two different days, performed in forty-four patients with different degrees of occlusive arterial disease, varied between 5.6 and 8.3 mmHg at the different levels. The present data indicate that the skin perfusion pressure on the legs in normal subjects lies approximately 10 mmHg lower than the systemic mean arterial blood pressure.