Why do patients with severe arterial insufficiency get pain during sleep?

Posture-induced intraocular pressure changes: considerations regarding body position in glaucoma patients

Although glaucoma is a multifactorial disease, elevated intraocular pressure (IOP) remains the most important known risk factor. Different systemic and local factors are thought to influence an individual's IOP. There can be a clinically significant rise in IOP when going from upright to horizontal or inverted body positions. Although there is a significant interindividual variability, the magnitude of the IOP change is greater in glaucomatous eyes. As patients usually spend a significant portion of their lives in the horizontal position, mainly during sleep, this is highly relevant. In this review we discuss the relationship between postural changes and IOP fluctuation, including changes in both body and head position. The possible mechanisms involved and the main implications for glaucomatous eyes are discussed. Finally, considerations with regard to sleep position in glaucoma patients are made based on evidence in the literature.

Nocturnal hypotension: role in glaucoma progression

The role of systemic blood pressure in glaucomatous damage remains undefined, with systemic hypertension and hypotension being implicated in different studies. We have previously reported that the physiologic nocturnal blood pressure "dip" may be exaggerated in some glaucoma patients with progressive field loss. A 24-hour ambulatory blood pressure recording was originally performed on 84 patients with glaucoma. The mean result across all our glaucoma patients were within the ranges reported in the literature for normal subjects. The normal-tension glaucoma and primary open-angle glaucoma groups did not differ significantly in blood pressure variables. Nocturnal blood pressure variables were lower in the patients with progressive field defects compared to those with stable visual fields. To determine long-term outcomes in these patients, we reevaluated the visual fields of the original 84 patients studied. In 70 patients with long-term visual field data (mean, 5.1 years), those who had shown greater nocturnal blood pressure dips were more likely to have shown field progression at some stage, despite good intraocular pressure control. Patients who had field progression showed significantly lower nocturnal blood pressure variables, with the dips of the systolic, diastolic, and mean arterial pressure significantly larger (systolic dip, P = 0.01). They also had a greater history of disk hemorrhages. A review of other 24-hour blood pressure studies in the literature shows that most are in agreement with these findings. The nocturnal reduction in blood pressure may, therefore, be an additional risk factor in glaucoma patients.

Ambulatory blood pressure monitoring in glaucoma. The nocturnal dip

PURPOSE

Hypoperfusion of the optic nerve head may be among the significant factors relating to glaucoma damage. The physiologic nocturnal blood pressure "dip" may be exaggerated in some patients and may compromise local vascular supply.

METHODS

Twenty-four-hour ambulatory blood pressure recording was performed on 38 patients with normal-tension glaucoma and on 46 with primary open-angle glaucoma. Eleven control subjects of similar age also were tested. The means of the systolic and diastolic blood pressures, mean arterial pressure, and pulse pressure for 24 hours, taken during the daytime (6 AM-10 PM) and night (10 PM-6 AM) periods were determined. The percentage nocturnal dip for each patient was calculated. A masked assessment of Humphrey visual fields for progression or stability was done on those 52 patients who had numerous fields plotted for more than 2 years.

RESULTS

The results of the control subjects confirmed that the authors' technique produces values similar to cardiologic studies from large healthy populations. The mean results from all the authors' patients with glaucoma were within the ranges reported for control subjects in the literature. The blood pressure parameters of the normal-tension glaucoma and primary open-angle glaucoma groups did not differ significantly. All nocturnal pressure parameters (except pulse pressure) were lower in the 37 patients with progressive field defects compared with the 15 patients whose pressure parameters were stable, whereas the systolic, diastolic, and mean arterial pressure dips were significantly larger (systolic dip, P = 0.001).

CONCLUSION

The nocturnal reduction in blood pressure may be an additional risk factor in patients with glaucoma.

Antihypertensive therapy and circadian blood pressure profiles: a retrospective analysis utilising cumulative sums

The results of previous studies on the effects of antihypertensive agents on circadian blood pressure patterns are inconclusive, possibly due to the lack of a simple, objective, universally accepted method of quantifying circadian blood pressure profiles. In order to investigate for differences in the effects of antihypertensive drugs on circadian changes we utilised a recently described modified cumulative sums technique to quantify circadian alteration magnitude (CAM). CAM is simply calculated as the difference between crest and trough blood pressures, the mean blood pressures of the 6-h periods of highest and lowest sustained pressures respectively. The records from all 24-h ambulatory blood pressure monitoring performed over a 7 year period on subjects either on no medication (1208), or on treatment with a single first-line antihypertensive agent (578), were examined retrospectively. A sample (n = 40) stratified for trough diastolic blood pressure, age and sex was randomly selected from each of the following 5 groups: subjects on no medication, and subjects being treated with bendrofluazide, atenolol, class 2 calcium-channel blockers or captopril alone. Untreated subjects, those on bendrofluazide and those on a class 2 calcium channel blocker had similar circadian patterns. Subjects on atenolol therapy (25.9 +/- 1.7/18.3 +/- 1.3, systolic CAM +/- SE/diastolic CAM +/- SE) had attenuated circadian changes (p < 0.05) when compared to the untreated group (29.8 +/- 1.8/23.6 +/- 1.1), while those on captopril (34.9 +/- 2.4/25.7 +/- 1.8) exhibited markedly increased systolic and diastolic circadian blood pressure swings, which differed from those of the atenolol treated group (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of gangrene during sleep

A method for continuous measurement of subcutaneous adipose tissue blood flow in the forefoot over 24 h (SBF) is described. The method is based on the radioisotope wash-out principle using 133-Xenon (133Xe). A portable semiconductor detector is placed just above a local depot of 37-74 kBq 133Xe in 0.1 ml isotonic saline, injected into the subcutaneous adipose tissue in the forefoot. The detector is connected to a memory unit allowing for storage of data. Because of the short distance, the recorded elimination rate constant must be corrected for combined convection and diffusion of the radioactive indicator. Characteristic 24-h blood flow patterns were unveiled in patients with normal peripheral circulation and in patients having ischaemic nocturnal rest pain. In normal subjects, SBF doubled from day to night. This is ascribed to the local veno-arteriolar sympathetic axon reflex, which induces vasoconstriction when the transmural pressure of the veins exceeds approximately 25 mmHg. In patients having ischaemic rest pains SBF was reduced by 37% on the average from day to night. This was caused by nocturnal hypotension, which is reflected proportionally in the foot. As the resistance vessels most probably are fully dilatated in feet with rest pain, the blood pressure drop during sleep causes the perfusion pressure and, therefore, blood flow to drop below a certain critical limit. There was a pronounced correlation between the reduction systemic mean arterial blood pressure and SBF. The patients complaining of intermittent claudication, but no rest pains, demonstrated a variety of changes in SBF compatible with the continuous spectrum of peripheral arteriosclerotic disease. The reduced blood flow during sleep in patients having ischaemic rest pains give rise to the concept of the development of gangrene during sleep.

[Morning rise in blood pressure: before or following awakening?]

The coincidence of the circadian peak of cardiovascular events with the morning blood pressure rise suggests causal connections. Rapidly acting antihypertensives taken before getting up may attenuate the increase early enough, if the onset does not occur before awakening. In 111 normotensives and in 109 subjects with untreated essential hypertension ambulatory blood pressure monitoring was performed to study whether the onset of the blood pressure rise occurs before or after waking up. The individual 24 h blood pressure profiles obtained by intermittent readings at intervals of 15 minutes were synchronized by the time of waking up. The resulting blood pressure curves showed no substantial blood pressure rise during sleep, but steep increases after awakening: Within the first hour after waking up blood pressure increased from 107.3 + 11.4/62.3 +/- 9.6 mm Hg (mean + sd) to 121.4 +/- 16.0/75.3 + 12.6 mm Hg in normotension and from 124.7 + 16.0/72.7 + 12.2 mm Hg to 140.3 + 17.2/84.5 + 13.3 mm Hg in hypertension. The velocity of this increase was dependent on the lag between waking up and getting up. There was no phase difference between early morning blood pressure and heart rate rises. Thus to attenuate the morning blood pressure increase, rapidly acting drugs after awakening may be considered instead of long acting antihypertensives administered prior to sleep.

Microvascular circulatory changes in the lower extremities after reconstructive vascular surgery for intermittent claudication

We have studied the circulatory changes in the lower extremities after reconstructive vascular surgery in ten patients with intermittent claudication. The following examinations were carried out 3 days before, 3 days, and 28 days after the operation: measurement of ankle systolic blood pressure, calf plethysmography, resting calf muscle blood flow and resting subcutaneous foot blood flow. The vasoconstrictor response (veno-arteriolar reflex) was also assessed. On the night before the operation and on the 28th night after aorto-bifemoral bypass surgery, subcutaneous adipose tissue blood flow in the forefoot was measured during sleep. The ankle systolic blood pressure and the ankle index rose significantly. The former increased from 57 +/- 16.4 mmHg to 93 +/- 24.0 mmHg (mean +/- S.E.M.) and was still elevated on the 28th postoperative day. The total limb blood flow, the muscle blood flow and the blood flow in the subcutaneous tissue of the forefoot during daytime were unchanged. In contrast, the blood flow in the forefoot during sleep increased significantly from 3.5 +/- 1.63 ml x (min x 100 g)-1 to 5.2 +/- 2.14 ml x (min x 100 g)-1 (mean +/- S.E.M.) on the 28th night. The vasoconstrictor response was potentiated, and increased from 27% before the operation to 45% on the third postoperative day. This change was maintained 28 days postoperatively. In conclusion the increase in arterial blood pressure was only reflected in the vasoconstrictor response which had returned to normal by the third postoperative day and nocturnal blood flow in the subcutaneous adipose tissue which did likewise.

The cause of ischaemic nocturnal rest pain

Adipose tissue blood flow in the forefoot was measured simultaneously with mean systemic arterial blood pressure over 24 hours in 8 patients (15 feet) with different degrees of arterial insufficiency. Mean systemic arterial pressure decreased by 19 +/- 9% during sleep, irrespective of symptomatology. In two limbs, with a normal peripheral circulation, blood flow decreased by 8 +/- 7%. In five limbs with arterial insufficiency, but no rest pain, blood flow decreased by 16 +/- 8% and in eight limbs with ischaemic nocturnal rest pain blood flow was reduced by 32 +/- 12% during sleep. It is concluded that nocturnal hypotension is a major factor in the production of nocturnal ischaemic rest pain.