Daniel Richardson

Fish oil increases peripheral capillary blood cell velocity in humans

Fish oils containing n-3 fatty acids have been shown in humans to decrease platelet aggregation in vitro, lower plasma triglycerides, and to increase bleeding time. The in vivo effects of fish oils on microcirculatory blood flow in humans has not been studied to date. Twenty-one male subjects were randomly assigned to either olive oil (n = 10) or fish oil (n = 11) supplemented groups to determine the effects of these oils on capillary blood flow velocity (CBV) in the nailfold area. The subjects were given the oils for three weeks (1.5 g oil/10 kg b.wt./day) in a single blind study design. In addition to CBV plasma lipid profiles, blood viscosity, blood pressure and platelet and erythrocyte fatty acids were also determined prior to and after the dietary intervention. Fish oil supplementation significantly increased CBV, by 1.75-fold (0.144 +/- 0.069 to 0.253 +/- 0.147 mm/s). The olive oil group remained unchanged. Increased levels of n-3 fatty acids were noted in platelets and erythrocytes of the fish compared to olive oil-supplemented groups. Blood viscosity was unaltered in both groups, however, blood pressure in the olive oil supplemented group was significantly decreased. Plasma triglycerides were significantly decreased in the fish oil supplemented group. These observations suggest that increases in CBV after fish oil supplementation are due to changes in vascular tone and not to alterations in blood pressure or blood viscosity.

Effects of Tobacco Smoke Inhalation on Capillary Blood Flow in Human Skin

To measure the effects of tobacco smoke inhalation on capillary blood flow in human skin, 20 female tobacco smokers consented to smoke three cigarettes with nicotine levels of 0.50, 0.98, and 1.90 mg per cigarette, each on a separate occasion. Measurements of blood flow velocity and vascular diameter were made along the venous limb of capillaries within the nailfold skin of the third finger via videomicroscopy before and for 5 min after the smoking of each cigarette. Capillary blood flow (CBF) was calculated as a product of capillary cross-sectional area and flow velocity. Resting pre-smoke CBF for all experiments combined averaged 4.7 X 10(4) mu 3/sec. All three cigarettes elicited a significant reduction in CBF with the maximal effect within the first 2 min of the post-smoke period (p less than or equal to .05). Respective CBF values during this time averaged 3.6, 3.4, and 2.7 mu 3/sec for the low-, medium-, and high-nicotine cigarettes. Although the data suggested a downward trend in CBF with increasing nicotine levels, the post-smoke values were not significantly different among the three cigarettes. It is concluded that acute tobacco smoke inhalation reduces CBF in human skin, but the effect is not related to the nicotine content of the cigarettes. The changes in cutaneous CBF observed with tobacco smoking are less compared to reported effects of smoke inhalation on total digital blood flow.

Don't dump the didactic lecture; fix it

Numerous articles have been published on the merits of active learning, and collectively they present a body of compelling evidence that these methods do enhance learning. In presenting arguments for active learning, it is often suggested that the traditional didactic lecture is more passive in nature and less effective as a teaching tool. However, a well organized lecture remains one of the most effective ways to integrate and present information from multiple sources on complex topics, such as those encountered in the teaching of physiology. This article presents an argument for enhancing lectures by incorporating active learning activities within their framework, and it is noted that engagement of the student is a key element making active learning activities work. Finally, suggestions are provided on the basis of the authors experience of things instructors can do to make lecture-based courses more engaging to students and, hence, promote learning.

Capillary blood flow: videodensitometry in the atherosclerotic patient.

Recently the noninvasive technique of videomicroscopy has demonstrated qualitative morphologic changes in the nutritional skin capillaries in atherosclerotic (ATS) patients. The purpose of this study is to quantitatively examine the ATS microcirculation and effects induced by reconstructive surgery. Capillary blood flow velocity (CBV) of single vessels within the nail fold of the large toe was measured by dual-sensor videodensitometry in 14 ATS patients (age 45 to 80 years) and 11 age-matched controls. In addition to CBV, capillary diameter (CD) and the number of flow-active capillaries (FC) were also measured at constant temperature. Of the 14 patients, eight had measurements repeated 1 week after reconstructive surgery. The measurements were obtained at rest and then periodically after a 45-second period of pedal inflow occlusion. Respective group averages at rest for CBV, CD, and FC for the 14 ATS patients were as follows: 0.16 mm/sec, 10.5 micron, and 6.8 capillaries per field. Corresponding values for the control subjects were 0.10 mm/sec, 8.7 micron, and 5.3 capillaries per field. Combining CBV, CD, and FC into a measurement of volume capillary flow yielded a value of 281 pl/sec/mm2 for the patients and only 85 pl/sec/mm2 for the controls (p less than 0.02). Peak postocclusion CBV significantly increased, whereas FC significantly decreased relative to rest in the control group; however, the only patient group that responded to occlusion-induced ischemia was the postoperative group. In these patients there was a decrease in CBV and an increase in FC relative to rest. These responses are exactly opposite to those in the age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Habitual Tobacco Smoking on Reactive Hyperemia in the Human Hand

The purpose of this study was to test the hypothesis that habitual smoking of tobacco cigarettes reduces reactive hyperemia in peripheral areas of smokers who are at low risk of having atherosclerotic vascular disease. This was achieved by a cross-sectional comparison of post-occlusion hyperemia in the hand circulation of female cigarette smokers and nonsmokers in the 20- to 40-yr age range. Epidemiologic evidence indicates that sclerotic lesions are unlikely in the upper extremities of females in this age range. The right hand of a subject was maintained in a water bath at 32 degrees C while mean blood flow velocity (V) in the radial artery was measured before and after occlusion periods of 1 and 5 min. The 5-min period elicited maximal reactive hyperemia. Following both periods of occlusion the percent increase in V was less for smokers (P less than .02). Also, the absolute increase in V following 5 min of occlusion for the smokers was less than that of the nonsmokers (P less than or equal to .05). These results indicate that habitual cigarette smoking reduces peripheral vasodilatory reserve in young smokers. The fact that sclerotic lesions are unlikely in the present subjects points to a microcirculatory rather than a macrocirculatory effect.

The cutaneous microcirculation of the forearm in young and old subjects

Previous studies have shown a reduced cutaneous circulatory response to direct heat stress in the forearm circulations of older (60 to 80 year) subjects. The purpose of this study was to test the hypothesis that this aging effect is due to a reduced ability of the cutaneous microvessels in the forearm to respond to direct heat. Two groups of male subjects consented to participate; a group of 15 young individuals (Y; 20-39 year) and a group of 11 older (O; 60-79 year) individuals. The subjects rested in a supine position with the right forearm situated on the stage of a Leitz epiilumination microscope which was used to view the superficial cutaneous microvessels. The width of the red cell column (WRC), an index of vascular diameter, and the blood cell velocity (BCV) within the microvessels were measured by videomicroscopy at the presenting skin temperature (Ts) of 32 degrees, and then again after Ts had been elevated to 35 degrees then 40 degrees. At a Ts of 32 degrees, WRC and BCV for the Y group, respectively, averaged 6.6 microns and 0.22 mm/sec. Corresponding averages for the O subjects were 8.4 microns and 0.17 mm/sec. Between-group differences were not significant. At a skin temperature of 40 degrees, BCV was significantly higher compared to that at 32 degrees and 35 degrees for both groups (P less than 0.05); whereas, WRC did not significantly change. There were no significant between-group differences in BCV at the higher two temperatures. These results argue against a diminished blood flow response of superficial microvessels being responsible for the reduced cutaneous circulatory response to heat stress in older individuals.

Relative effects of static muscle contraction on digital artery and nailfold capillary blood flow velocities

Previous studies have shown that a decrease in blood flow to the finger is not necessarily accompanied by a corresponding change of blood flow in nailfold capillaries. The purpose of this study was to determine if nailfold capillary blood flow remains relatively stable during a decrease in finger blood flow induced by muscle contractions. Four male subjects 20 to 30 years of age exerted 2-min periods of static calf muscle contraction at levels of 7.5, 15, 30, and 45% of their maximum voluntary contractile force (MVC) while systemic blood pressure (BP), and flow velocities in the digital artery (VEL-A) and nailfold capillaries (VEL-C) were measured by, respectively, Doppler ultrasound and video densitometry. Each subject repeated the series five times. There was a significant linear decrease in VEL-A with increasing force of contraction for each subject individually (P less than or equal to 0.009) and for the group as a whole (P less than or equal to 0.0001); whereas VEL-C did not significantly change during muscle contraction. These results indicate that the initial cutaneous constrictor response in the finger during the onset of leg muscle exercise is not reflected to the nailfold capillaries.

Effects of gravity on regional and capillary blood flows in the human toe.

The purpose of this study was to investigate the relative effects of gravity on capillary and regional blood flows in human extremities. Eighteen male subjects 20 to 40 years of age consented to have capillary blood cell velocity (CBV) measured in nailfold vessels of the large toe via video densitometry, and to have total blood flow (TBF) to the toe measured via plethysmography. These measurements were made first with the foot at heart level (HL), then after the foot had been lowered an average of 56 cm below the heart (BH). In the HL position CBV and TBF averaged respectively 0.26 mm/sec and 2.0 ml/min/100 ml. Lowering the foot elicited a decrease in CBV in all vessels studied (P less than or equal to 0.001). Average CBV in the BH position was 0.11 mm/sec. By contrast TBF on the average increased to 2.9 ml/min/100 ml in the BH position (P less than or equal to 0.05). However, this was not a consistent finding since both increases and decreases in TBF were observed among the individual subjects. These results indicate that the immediate precapillary vessels in the cutaneous circulation of the toe will consistently vasoconstrict when the foot is placed in a dependent position. However, the net effect on vessels governing regional flow in this area, e.g., A-V shunts, appears to result from a competition between dilator and constrictor influences. The overall result of these adjustments is that during orthostasis blood is shifted away from the superficial capillaries of the lower extremities. The relevance of this to blood-tissue fluid balance is discussed.

Effects of ischemia on capillary density and flow velocity in nailfolds of human toes

The purpose of this study was to investigate reactive hyperemia in the capillary network of human skin in terms of the flow per capillary and the density of flow-active capillaries. Seventeen male subjects 20 to 40 years of age were seated with their right foot placed on the stage of a Leitz epi-ilumination microscope such that the nailfold capillary field in their large toes could be viewed. These vessels were video taped while flow velocity in the right posterior tibial artery was recorded via Doppler ultrasound at rest, then following a 45-sec period of arterial occlusion to the foot. Subsequent to experimentation flow velocity in single nailfold capillaries was measured via video densitometry and the number of flow-active capillaries in the field of view were counted. Following the release of arterial occlusion arterial flow velocity increased 142% above rest, the velocity in single capillaries increased by 54%, and the density of flow-active capillaries, as identified by the presence of red cells, decreased by 37%. The fact that capillary flow velocity increased to a lesser degree than arterial velocity during reactive hyperemia vis-a-vis a decrease in the number of flow-active capillaries indicates that ischemia to the foot elicits a smaller dilatory effect in vascular elements controlling blood flow to the superficial cutaneous region of the toe as compared to other regional vascular networks.

Comparison of capillary blood flow in the nailfold circulations of young and elderly men

This study investigated the effects of aging on capillary dynamics in the human skin by comparison of capillary blood flow velocity (CBV), capillary diameter and volume capillary blood flow (CBF) in the looped capillaries within the dermal papillae of nailfolds in young (Y — mean age 26 yr) and elderly (E — mean age 63 yr) male subjects. Both toe and finger nailfolds were studied. Quantitative measurements were made only in vessels with relatively straight arterial and venous branches. However, qualitative comparisons were also made of the number of capillaries per field and the general structure of the capillaries. Flow velocity (CBV) was significantly lower in both the toe and finger nailfolds of the E compared to the Y subjects (P≤ 0.050). There was no significant difference in capillary diameter, therefore, volume flow (CBF) was also lower in the E subjects. Respective values of CBF in the toe nailfolds of the Y and E groups were: 1.41 × 104 u3/sec and 0.76 × 104 u3/sec (P ≤ 0.075). Corresponding values for the finger nailfolds were: 2.27 × 104 u3/sec and 1.35 × 104 u3/sec for the Y and E subjects (P ≤ 0.050). There were no significant differences in the number of capillaries per field between the groups although there was a trend towards fewer vessels in the toe nailfolds of the elderly. The elderly also had a higher percentage of tortuous vessels in their toe nailfolds compared to the Y subjects. This observation vis-a-vis a tendency towards fewer vessels in the toe nailfolds of the E subjects indicates that aging may have a more pronounced effect on total capillary flow in this region than indicated by CBF alone.