J. P. Woodcock

Neovascularization in human cutaneous melanoma: A quantitative morphological and Doppler ultrasound study

A study of tumour blood flow in 36 patients with 38 malignant melanomas using Doppler Ultrasound flowmetry has shown that tumour blood flow can be detected in most melanomas more than 0.9 mm thick, and is absent in most melanomas less than this thickness. Histological quantitation of blood vessels using lectin staining to delineate vascular endothelium and automated image analysis has shown a high degree of correlation between vascularity at the tumour base and tumour thickness. Since it is likely that the development of a vascular plexus at the tumour base is a prerequisite for dissemination, the development of these blood vessels may prove to be an independent prognostic factor for thin melanomas. This work also provides a new model for dynamic, in vivo investigation of the vascularity of human tumours.

Measurement of volume flow in the human common femoral artery using a duplex ultrasound system.

A duplex ultrasound system was used to measure volumetric flow in the human common femoral artery. The accuracy of the technique was validated using a flow rig. The average resting common femoral artery flow rate in a population of subjects clinically unaffected by peripheral vascular disease was 350 +/- 141 mls min-1. Although mean common femoral artery diameter was greater in males (10 +/- 0.9 mm) than in females (7.8 +/- 0.7 mm) (p less than 0.01), there was no significant difference in resting blood flow. Repeated measurements in individual subjects showed a high variability, largely due to physiological fluctuations (75 percent of total variability). There was a close correlation between volume flow and the reciprocal of pulsatility index (100/PI). In normal subjects 100/PI represents a simpler method of determining individual changes in blood flow. The temporal variations in volume flow during periods of reactive hyperaemia had a characteristic profile, which was dependent on the duration of circulatory arrest. The data derived from the resting hyperaemia flow profile provides normal ranges for future comparison with patients suffering from peripheral vascular disease.

Principles of Physics in Surgery: The Laws of Mechanics and Vectors Physics for Surgeons—Part 2

In this sequel, to an earlier article, we discuss the laws of Mechanics, Thermodynamics and Vectors as they apply to soft and bony tissues. These include the Laplace’s Law as applied to colonic perforation, compression therapy, parturition, variceal rupture, disc herniations etc. The Pascal’s Law finds use in hernia repair and the Heimlich maneuver. Trigonometrically derived components of forces, acting after suturing, show ways to reduce cut-through; the thickness and the bite of suture determines the extent of tissue reaction. The heating effect of current explains the optimum gap between the prongs of a bipolar cautery and the use of law of transfer of heat in determining relation between healthy wound healing and ambient temperature.

Postural changes in femoral artery blood flow in normal subjects, patients with peripheral vascular occlusive disease and patients undergoing lumbar sympathectomy, measured by duplex ultrasound flowmetry.

Regulatory peripheral vasoconstriction occurs in response to lower limb dependency. In mildly ischaemic limbs these responses are retained but are lost in patients with rest pain. Previously used methods have inherent difficulties when applied during postural change. We studied orthostatic responses in 12 normal subjects (aged 22-74 years, median 52 years) and 16 patients (aged 21-83 years, median 48 years) with mild and severe peripheral vascular disease using a duplex ultrasound flowmeter. In the normal subjects the 60-s mean common femoral artery volume flow values (ml min-1 +/- S.D.) were 77 +/- 83; -78 +/- 116; -190 +/- 136 for elevation, dependency and standing respectively. For claudicants (n = 7) the values were 18 +/- 37; -112 +/- 123; -216 +/- 103, respectively. In rest pain patients (n = 9) the responses were reversed, being -252 +/- 124; 131 +/- 89 and 184 +/- 85. Significant differences were apparent between elevation, dependency and standing flows, in each of the three groups (all p less than 0.0001). The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants, for each postural change (p less than 0.0001 in all cases). Investigation of the dependency response was undertaken in eight further patients with rest pain before and after lumbar chemical sympathectomy and a characteristic pre-sympathectomy response predicted the clinical outcome.

Principles of physics in surgery: the laws of flow dynamics physics for surgeons — Part 1

In the field of medicine and surgery many principles of physics find numerous applications. In this article we have summarized some prominent applications of the laws of fluid mechanics and hydrodynamics in surgery. Poiseuille’s law sets the limits of isovolaemic haemodilution, enumerates limiting factors during fluid resuscitation and is a guiding principle in surgery for vascular stenoses. The equation of continuity finds use in non-invasive measurement of blood flow. Bernoulli’s theorem explains the formation of post-stenotic dilatation. Reynolds number explains the origin of murmurs, haemolysis and airflow disturbances. Various forms of oxygen therapy are a direct application of the gas laws. Doppler effect is used in ultrasonography to find the direction and velocity of blood flow. In this first part of a series of articles we describe some applications of the laws of hydrodynamics governing the flow of blood and other body fluids.

Intermittent venous compression, and the duration of hyperaemia in the common femoral artery

External compression of limbs to below‐diastolic pressure (venous compression) has been shown to produce a short‐lived hyperaemia in supply arteries. Intermittent pneumatic compression is currently under investigation therefore as a treatment for peripheral arterial disease. The optimal timing of the compression will depend on the duration of hyperaemia produced by a particular duration of compression, and the purpose of this work was to test that link. Nineteen healthy volunteers underwent intermittent compression of one leg with two compression cycles – one compressing for 10 s each time, the other for 1 min. Blood flow velocities in the common femoral artery was shown to increase on release of the compression by 38% (inter‐quartile range 27–56%) for the sequence with short duration compression, and by 57% (inter‐quartile range 37–87%) for the longer sequence (difference, P = 0·005, Wilcoxon). The hyperaemia duration above the baseline level was 37 s (inter‐quartile range 32–49 s) for the short sequence, and 54 s (inter‐quartile range 37–76 s) for the longer sequence (difference, P = 0·001, Wilcoxon). The magnitude of the change in the compression duration was not equalled by the difference in hyperaemia duration, suggesting that the physiological mechanism behind the hyperaemia is unlikely to be due solely to simple accumulation of metabolites, and a myogenic mechanism remains possible. Therapies for peripheral arterial disease need not employ long duration compression, as a greater percentage of time will be spent in hyperaemia with short duration intermittent compression.

Analysis of the operation of the SCD Response intermittent compression system

The work assessed the performance of the Kendall SCD Response intermittent pneumatic compression system for deep vein thrombosis prophylaxis, which claimed to set its cycle according to the blood flow characteristics of individual patient limbs. A series of tests measured the system response in various situations, including application to the limbs of healthy volunteers, and to false limbs. Practical experimentation and theoretical analysis were used to investigate influences on the system functioning other than blood flow. The system tested did not seem to perform as claimed, being unable to distinguish between real and fake limbs. The intervals between compressions were set to times unrealistic for venous refill, with temperature changes in the cuff the greatest influence on performance. Combining the functions of compression and the measurement of the effects of compression in the same air bladder makes temperature artefacts unavoidable and can cause significant errors in the inter-compression interval.

Effect of postural change on common femoral artery volume flow, measured by duplex ultrasound, in normal subjects and patients with peripheral vascular disease

Regulatory peripheral vasoconstriction occurs in response to adoption of the erect posture. Mildly ischaemic limbs are thought to exhibit near normal responses, but patients with rest pain show increases in blood flow on limb dependency. Previous methods of limb blood flow quantification (xenon clearance and venous occlusion plethysmography) have inherent difficulties when applied in these situations. We studied orthostatic responses in 12 normal subjects (aged 22-74 years (median 52) and 16 patients (aged 21-83 (median 48) with mild and severe peripheral vascular disease, using a duplex flowmeter system. In the normal subjects changes in the 60s mean, common femoral artery volume flow values were as follows (ml min-1 (1 SD]: 77 (83), -78 (116) and -190 (136), for elevation, dependency, and standing respectively. For claudicants (n = 7) the values were 18 (37), -112 (123) and -216 (103) respectively. In rest pain patients (n = 9) the responses were reversed, being -252 (124), 131 (89) and 184 (85) respectively. Significant differences were apparent between elevation, dependency and standing flows in each of the three groups (P less than 0.0001). Normal subject and claudicant responses on elevation and dependency differed significantly (P less than 0.0001 and 0.03 respectively). On standing, the responses were similarly significantly different. The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants for each postural change (P less than 0.0001 in all cases). Duplex ultrasound volume flowmetry is non-invasive and offers an excellent method of quantifying physiological changes.

Digital and radial artery blood flow in patients with Raynaud's phenomenon in response to nifedipine

The effect of nifedipine on haemodynamic changes in the hand after cooling in 10 patients with Raynauds phenomenon is assessed. Nifedipine reduced the fall in digit blood flow induced by cooling and limited the increase in pulsatility index (a measure of peripheral resistance). There was good correlation between digital arterial inflow (measured by strain gauge plethysmography) and radial artery pulsatility index (measured by Doppler waveform analysis).

Spatial-temporal display of colour-flow ultrasound for the assessment of the effects of intermittent pneumatic compression in limbs.

Colour-flow M-mode ultrasonography in three dimensions (two spatial, one temporal) was used to assess the effects of intermittent pneumatic compression on the blood flow velocities in the common femoral vein and artery. The linear array of a standard 3-D system was held in place over the vessels, to record while a calf and thigh cuff compressed to 60 mmHg. The data was reconstructed in 3-D and, subsequently, sliced in different planes. The technique effectively demonstrated the emptying of distal veins during compression, and hyperaemia in the artery on deflation, in the coronal and sagittal planes. Reconstructions of this type may be of use in visualising the distribution of flow changes within blood vessels.