Alkalosis-induced coronary vasoconstriction: effects of calcium, diltiazem, nitroglycerin, and propranolol

Is Chronic Fatigue Syndrome Synonymous with Effort Syndrome?

Chronic fatigue syndrome (CFS), including myalgic encephalomyelitis (ME) and postviral syndrome (PVS), is a term used today to describe a condition of incapacity for making and sustaining effort, associated with a wide range of symptoms. None of the reviews of CFS has provided a proper consideration of the effort syndrome caused by chronic habitual hyperventilation. In 100 consecutive patients, whose CFS had been attributed to ME or PVS, the time course of their illness and the respiratory psychophysiological studies were characteristic of chronic habitual hyperventilation in 93. It is suggested that the labels ‘CFS’, ‘ME’ or TVS' should be withheld until chronic habitual hyperventilation - for which conventional rehabilitation is available - has been definitively excluded.

Drug-induced acid-base disorders

The incidence of acid-base disorders (ABDs) is high, especially in hospitalized patients. ABDs are often indicators for severe systemic disorders. In everyday clinical practice, analysis of ABDs must be performed in a standardized manner. Highly sensitive diagnostic tools to distinguish the various ABDs include the anion gap and the serum osmolar gap. Drug-induced ABDs can be classified into five different categories in terms of their pathophysiology: (1) metabolic acidosis caused by acid overload, which may occur through accumulation of acids by endogenous (e.g., lactic acidosis by biguanides, propofol-related syndrome) or exogenous (e.g., glycol-dependant drugs, such as diazepam or salicylates) mechanisms or by decreased renal acid excretion (e.g., distal renal tubular acidosis by amphotericin B, nonsteroidal anti-inflammatory drugs, vitamin D); (2) base loss: proximal renal tubular acidosis by drugs (e.g., ifosfamide, aminoglycosides, carbonic anhydrase inhibitors, antiretrovirals, oxaliplatin or cisplatin) in the context of Fanconi syndrome; (3) alkalosis resulting from acid and/or chloride loss by renal (e.g., diuretics, penicillins, aminoglycosides) or extrarenal (e.g., laxative drugs) mechanisms; (4) exogenous bicarbonate loads: milk-alkali syndrome, overshoot alkalosis after bicarbonate therapy or citrate administration; and (5) respiratory acidosis or alkalosis resulting from drug-induced depression of the respiratory center or neuromuscular impairment (e.g., anesthetics, sedatives) or hyperventilation (e.g., salicylates, epinephrine, nicotine).

Evaluation and treatment of respiratory alkalosis

Respiratory alkalosis is the most frequent acid-base disturbance encountered in clinical practice. This is particularly true in critically ill patients, for whom the degree of hypocapnia directly correlates with adverse outcomes. Although this acid-base disturbance often is considered benign, evidence suggests that the alkalemia of primary hypocapnia can cause clinically significant decreases in tissue oxygen delivery. Mild respiratory alkalosis often serves as a marker of an underlying disease and may not require therapeutic intervention. In contrast, severe respiratory alkalosis should be approached with a sense of urgency and be aggressively corrected.

Changes in pH Increase Perfusion Pressure of Coronary Arteries in the Rat

Stricture of coronary arteries is closely related to ischemic heart disease. The purpose of this study was to examine whether changes in pH caused contraction of rat coronary arteries, as determined using Langendorff perfused hearts. Changing the pH of the perfusate increased perfusion pressure as an indication of the contractile state of coronary arteries. Alkaline pH-induced increase of perfusion pressure in Wistar Kyoto rats (WKY) was almost identical to that of spontaneously hypertensive rats (SHR), whereas acidic pH-induced increase in SHR was much greater than that in WKY. Acidic pH-induced increase in perfusion pressure was inhibited by verapamil, cromakalim, and adenosine. Feeding WKY with N(G)-nitro-L-arginine resulted in hypertension followed by enhanced acidic pH-induced increase in perfusion pressure. These results suggest that acidic-pH induced contraction of rat coronary arteries is caused by Ca(2+) influx through voltage-dependent Ca(2+) channels and the contraction is enhanced by hypertension.

Changes in autonomic nervous activity prior to spontaneous coronary spasm in patients with variant angina

Although the autonomic nervous system has been implicated in the genesis of coronary spasm, the precise mechanism by which it serves as the trigger of coronary spasm remains unclear. The aim of this study was to investigate changes in autonomic nervous activity associated with ischemic episodes in patients with variant angina (VA). Heart rate variability (HRV) on Holter monitoring was analyzed during 17 ischemic episodes in 11 patients with VA. The parameters of HRV were measured during a 2-min period at various time intervals prior to the onset of ST-segment elevation. The low frequency (LF) and high frequency (HF) components of the HRV, LF/HF ratio, mean RR interval, and the coefficient of the RR interval variation (CV) were calculated for each time interval. Both the HF and the CV increased significantly in the 2 min prior to the onset of ST-segment elevation, suggesting heightened vagal activity. The LF/HF ratio, a measure of cardiac sympatho-vagal balance, did not change. The LF, a measure of sympathetic activity with vagal modulation, also did not change. The RR interval decreased significantly in the 2 min prior to the onset of ST-segment elevation. These results suggest that enhancement of both the vagal and the sympathetic nervous activity plays an important role in the initiation of coronary spasm.

Combined effects of hypocapnia and nicardipine on airway resistance: a pilot study

OBJECTIVE

The aim of this study was to investigate the modification of the resistive inspiratory properties of the respiratory system associated with hypocapnia in the presence of nicardipine.

METHODS

The resistance of the respiratory system, Rrsmin, was studied in two groups of patients who needed mechanical hyperventilation. Group 1 (n = 14; 47 years) was the control group (head injuries); group 2 (n = 12; 53.5 years) included patients treated over a 3 week period with nicardipine (0.5 microgram.kg-1.min-1 i.v.) to prevent arterial vasospasm after subarachnoid haemorrhage.

RESULTS

There was no statistical difference between the groups concerning anthropometric and basal respiratory characteristics. In group 1, hypocapnia caused a 20.9% increase in Rrsmin, but no significant increase was observed in group 2.

CONCLUSION

Hypocapnic alkalosis had a significant bronchial constrictory effect, which was eliminated in the presence of nicardipine hydrochloride.

Hyperventilation in Patients Who Have Sustained Myocardial Infarction after a Work Injury

Patients who present with acute myocardial infarction after a work injury (AMI-WI) often report symptoms consistent with chronic hyperventilation which date back as far as the work injury itself, rather than to the AMI. The aim of the study was to test the hypothesis that hyperventilation significantly contributes to the symptoms of AMI-WI patients.

The prevalence of hyperventilation was assessed by clinical capnography in 12 AMI-WI patients, 20 normal controls, 15 AMI patients whose AMI was conventional and not subsequent to a work injury (AMI-C) and 14 patients with post-traumatic stress disorder (PTSD). End-tidal carbon dioxide partial pressure (PetCO2) was measured at rest, after 1 min hyperventilation (FHPT), after recall of the relevant stressor (Think) and when the breathing was felt to be normal (MBIN).

PetCO2 levels after FHPT were: 29.0±1.5 (mean±SD) mmHg for AMI-WI; 26.7±1.9 mmHg for PTSD; 32.1± 4.1mmHg for AMI-C and 33.7±1.4 mmHg for the controls ( P< 0.05 and P< 0.01 for AMI-WI and PTSD, respectively, versus controls). After Think, the levels were 25.8±1.6 mmHg for AMI-WI, 24.6±1.4 mmHg for PTSD, 31.2±4.1mmHg for AMI-C and 31.2± 1.5 mmHg for normals ( P<0.05 and P<0.01 for AMI-WI and PTSD, respectively, versus controls). For MBIN, values of PetCO2 were 26.8±1.7 mmHg and 26.7±1.5mmHg for AMI-WI and PTSD versus 33.8±1.2 mmHg for normals, ( P< 0.01 for both versus controls). Ten AMI-WI and 12 PTSD were positive for hyperventilation versus four AMI-C patients and four controls ( P< 0.01). The implications for rehabilitation, compensation and pathophysiology of AMI-WI are discussed, both from a medical-scientific perspective and in terms of admissible legal evidence.

Calcium channel current of vascular smooth muscle cells: extracellular protons modulate gating and single channel conductance

Modulation of L-type Ca2+ channel current by extracellular pH (pHo) was studied in vascular smooth muscle cells from bovine pial and porcine coronary arteries. Relative to pH 7.4, alkaline pH reversibly increased and acidic pH reduced ICa. The efficacy of pHo in modulating ICa was reduced when the concentration of the charge carrier was elevated ([Ca2+]o or [Ba2+]o varied between 2 and 110 mM). Analysis of whole cell and single Ca2+ channel currents suggested that more acidic pHo values shift the voltage-dependent gating (approximately 15 mV per pH-unit) and reduce the single Ca2+ channel conductance gCa due to screening of negative surface charges. pHo effects on gCa depended on the pipette [Ba2+] ([Ba2+]p), pK*, the pH providing 50% of saturating conductance, increased with [Ba2+]p according to pK* = 2.7-2.log ([Ba2+]p) suggesting that protons and Ba2+ ions complete for a binding site that modulates gCa. The above mechanisms are discussed in respect to their importance for Ca2+ influx and vasotonus.

Evidence for pH as an important parameter to control when studying the contractility of isolated rabbit cerebral arteries

Isolated rabbit basilar (BA), middle (MCA) and posterior (PCA) cerebral arteries mounted in an isometric Mulvany myograph and stretched to a given level of resting tension, developed a spontaneous slow-rising contraction. This tone presented the main features of a classical myogenic tone since it was not suppressed by repetitive washings, was not dependent on the presence of endothelium and was markedly influenced by the concentration of extracellular calcium. In addition, we observed that the occurrence of myogenic tone was dependent on the pH of the medium buffer. Decreasing pH of the Krebs solution from 7.54 to 6.81 by lowering NaHCO3 concentration from 25 to 5 mM, reduced the amplitude of the myogenic tone developed by the arteries. We investigated the influence of such changes of pH on the contractile response to potassium chloride (KCl) and to 5-hydroxytryptamine (5-HT). We demonstrated that the contractile response to KCl (124 mM) was not affected by the pH of the organ bath whereas the maximum contraction to 5-HT (10 microM) was significantly affected in BA but not in MCA and PCA. Furthermore, we found that three consecutive concentration-response curves to 5-HT were reproducible when obtained at pH 7.15 and 7.30 for BA and MCA. In PCA, 5-HT-induced responses were reproducible at pH 7.30 whereas the sensitivity of the repeated response curves to 5-HT was reduced at pH 7.15. We also noted a larger variability of the response to 5-HT for the three arteries at this pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of hyperventilation-induced attacks with infusion of atrial natriuretic peptide in patients with variant angina pectoris

Atrial natriuretic peptide (ANP) is reported to dilate a major coronary artery in both experimental animals and humans. Spasm of a major coronary artery is the cause of variant angina pectoris and can be induced by hyperventilation. The effect of the ANP infusion on anginal attack induced by hyperventilation was studied in patients with variant angina pectoris. The study was performed in the early morning on 3 consecutive days in 11 patients with variant angina pectoris in whom the attacks were reproducibly induced by hyperventilation. On days 1 and 3 (saline solution infusion), and day 2 (ANP infusion), hyperventilation was started 14 minutes after beginning infusion of ANP (0.1 microgram/kg/min) or saline solution for 6 minutes. The attacks were induced in all 11 patients by hyperventilation on days 1 and 3. However, the attacks were not induced in any patient on day 2 of the ANP infusion. The plasma ANP level increased from 33 +/- 7 pg/ml to the peak level of 2,973 +/- 479 pg/ml (p < 0.01) at the end of the ANP infusion, and the plasma level of cyclic guanosine monophosphate (cGMP) increased from 5 +/- 1 pmol/ml to the peak level of 58 +/- 6 pmol/ml (p < 0.01) 5 minutes after the ANP infusion. The plasma levels of ANP and cGMP did not change after hyperventilation on days 1 and 3. It is concluded that the ANP infusion suppresses the attacks induced by hyperventilation in patients with variant angina pectoris, and cGMP is related to the mechanisms of suppression of the attacks.

Systemic vasomotor interaction between nicardipine and hypocapnic alkalosis in man

The effects of hypocapnic alkalosis on the vasodilating action of nicardipine were studied in 6 patients after cerebral arterial aneurysm surgery. Each patient served as his/her own control during the 6 steps of the study. T0: baseline; T1: hypocapnic alkalosis alone (PaCO2: 3.5 kPa); T2: hypocapnic alkalosis and bolus injection of nicardipine (30 micrograms.kg-1 i.v.); T3: hypocapnic alkalosis and continuous 60 min infusion of nicardipine (0.5 microgram.kg-1.min-1), T4: determination of the infusion rate required to neutralize the effect of hypocapnic alkalosis; T5: same continuous dose of nicardipine as in T4 but reversal of hypocapnic alkalosis. Hypocapnic alkalosis alone caused a significant increase in the systemic vascular resistance index by 20% (T1). The bolus injection of nicardipine reversed this first effect (T2). The continuous infusion of nicardipine in T3 was insufficient to cancel the haemodynamic effect of hypocapnic alkalosis. During T4 the plasma levels required to neutralize completely the effect of hypocapnic alkalosis were twice those at T3. Normalization of the PaCO2 in step T5 induced a significant fall in the systemic vascular resistance index by 27.5% as compared with T0. In this study hypocapnic alkalosis modified the relationship between plasma levels of nicardipine and its expected vasoactive effects. This interaction was reversible.

Combined effects of nicardipine and hypocapnic alkalosis on cerebral vasomotor activity and intracranial pressure in man

The effect of hypocapnic alkalosis (HA) on nicardipine-induced cerebral vasodilatation was studied in 2 groups of patients undergoing stereotaxic brain biopsy under general anaesthesia. Arterial diameter (AD) was measured in 16 different locations on a carotid arteriogram (lateral view), and intracranial pressure (ICP) was recorded with an intraventricular catheter. At time T0, in normocapnia an arteriogram was performed in both groups. The first group (GI) was then studied in hypocapnia (T1) and following an injection of nicardipine (T2), while the second group (GII) was studied first after injection of nicardipine (T1) and then in hypocapnia (T2). Groups GI (n = 6; 44 y) and GII (n = 6; 46 y) were similar with regard to age, blood pressure, heart rate and PaO2 at all three phases of the study. HA caused a 9.5% decrease in AD (GI.T1) compared to baseline values, and a 15.2% decrease when preceded by injection of nicardipine (GII.T2). In the latter case the decrease was 3% in comparison with baseline. Nicardipine increased AD by 14.7% (GII.T1) and by 18.5% when preceded by HA (GI.T2), but the rise (7.3%) was not significant in comparison with the baselines value. The changes variations were similar whether the entire arterial trunk or only the supraclinoid region were studied. HA decreased ICP by 44% (GI.T1) and by 50% after nicardipine (GII.T2). Nicardipine did not cause an increase in ICP. Nicardipine and HA antagonise each others vasomotor effects, as previously shown in the baboon using nimodipine.

H(+)-induced vasodilation of rat aorta is mediated by alterations in intracellular calcium sequestration

Acidosis induces vasodilation both in vivo and in vitro. Although it is commonly surmised that acidosis alters contractility by affecting contractile proteins and calcium entry, the exact role of these mechanisms in acidosis-induced vasodilation has not been determined. In the present study, we demonstrated that a novel mechanism, involving increased calcium sequestration into intracellular sites sensitive to norepinephrine, mediates the vasodilation associated with relatively modest decreases in pH. The effects of changing pH from 7.4 to 7.0 on tension development, 45Ca fluxes, and the norepinephrine-releasable intracellular calcium stores were studied in isolated rat aorta. Acute acidification produced marked endothelium-independent dilations of aortic rings that had been precontracted with norepinephrine. In contrast, this maneuver had only modest effects on contractions elicited by 80 mM KCl or phorbol ester. Acidification in this range did not alter basal or norepinephrine-stimulated undirectional 45Ca influx, nor did it reduce the norepinephrine-induced net gain in 45Ca content. Furthermore, neither norepinephrine-stimulated 45Ca efflux nor the peak contractile response to norepinephrine in calcium-free buffer was affected, although in this setting, the duration of the phasic contractile response was shortened. When calcium was restored to tissues exposed to norepinephrine in calcium-free buffer, acidification slowed the rate of tension development without altering 45Ca uptake, thus changing the relation between tension development and calcium entry. These effects of acidification were shown to be associated with an increase in the amount of calcium sequestered into the norepinephrine-sensitive intracellular calcium store. These findings clearly indicate that acidification, within a range that has no effect on other aspects of smooth muscle activation, elicits vasodilation by stimulating intracellular calcium sequestration. This action may represent a predominant mechanism whereby acidosis alters vascular smooth muscle contractility.

Effects of magnesium on the tone of isolated human coronary arteries. Comparison with diltiazem and nitroglycerin

To study the effects of magnesium (Mg2+) on human coronary arteries and to compare those effects with those of diltiazem and nitroglycerin, we measured the tension of ring segments from isolated human coronary arteries obtained at autopsy within 5 hours after death. Precontracted segments with 3 x 10(-6) M prostaglandin F2 alpha were studied after adding cumulative concentrations of these agents (1.0-8.0 mM, 10(-9)-10(-5) M, and 10(-10)-10(-6) M, respectively). Mg2+ significantly inhibited the tonic contraction compared with the time-matched controls at 1.0 and 2.0 mM (48.7 +/- 5.6% vs. 88.6 +/- 2.2%, p less than 0.01, 36.2 +/- 6.1% vs. 78.9 +/- 3.0%, p less than 0.01, respectively). 1.0 and 2.0 mM Mg2+ did not suppress, but actually increased, the amplitude of periodic contraction, but 8.0 mM Mg2+ reduced the amplitude compared with the controls (6.6 +/- 5.2% vs. 73.3 +/- 10.7%, p less than 0.01). Diltiazem at a concentration of 10(-5) M moderately inhibited the tonic contraction, and reduced the amplitude of periodic contraction almost completely. Nitroglycerin reduced the tonic contraction almost completely at a concentration of 10(-6) M but did not reduce the amplitude of periodic contraction at any concentration. We conclude that 1.0 and 2.0 mM Mg2+ inhibits the tonic contraction and that 8.0 mM Mg2+ inhibits the periodic as well as the tonic contraction of isolated human coronary arteries. Diltiazem inhibits the periodic contraction, whereas nitroglycerin suppresses tonic contraction without affecting the periodic contraction.

Effect of magnesium on anginal attack induced by hyperventilation in patients with variant angina

To examine whether or not magnesium suppresses coronary spasm, the effect of magnesium infusion on anginal attacks induced by hyperventilation was studied in 20 patients with variant angina. In all patients, anginal attacks associated with ischemic ST segment changes on the electrocardiogram were repeatedly induced by hyperventilation. The study was performed in the early morning successively for 3 days. On days 1 and 3 (control studies), 50 minutes before the hyperventilation test, a 5% glucose solution was infused as a placebo. On day 2 (magnesium study), 50 minutes before the hyperventilation test, magnesium sulfate (0.27 mM/kg body wt) was infused during a 20-minute period. During the control studies, anginal attack was induced by hyperventilation in all 20 patients, whereas during the magnesium study, anginal attack was induced by hyperventilation in only six (30%) of the 20 patients (p less than 0.001 vs. control studies). The changes in arterial blood pH and PCO2 caused by hyperventilation were not significant between the control study and the magnesium study. Mean serum magnesium concentration increased from 2.2 +/- 0.2 to 6.0 +/- 0.5 mg/dl immediately after infusing magnesium and was 4.5 +/- 0.6 mg/dl before the hyperventilation test during the magnesium study. We conclude that magnesium suppresses anginal attacks induced by hyperventilation in patients with variant angina.

Hyperventilation-induced simultaneous multivessel coronary spasm in patients with variant angina: an echocardiographic and arteriographic study

Left ventricular wall motion abnormalities during an attack of coronary spasm induced by hyperventilation were examined with use of two-dimensional echocardiography in 27 patients with variant angina. Transient abnormal wall motion (asynergy) confined to one coronary artery region was found in 18 of the 27 patients and transient abnormal motion extending over more than one coronary artery region in the remaining 9 patients. Spasm of more than one major coronary artery was demonstrated separately by coronary arteriography during an attack induced by injection of acetylcholine or ergonovine in seven of the nine patients who manifested asynergy in more than one coronary artery region. In one patient, spasm was demonstrated in one major coronary artery, and the other coronary arteries were severely stenosed or occluded organically. In the remaining patient, acetylcholine was not injected into both arteries; however, the attack was sometimes associated with ST segment elevation in the anterior leads and at other times in the inferior leads. Therefore, simultaneous multivessel coronary spasm seems to have occurred in eight of the nine patients who exhibited asynergy in more than one coronary artery region. The 8 patients with simultaneous multivessel coronary spasm had a higher degree and longer duration of ST segment elevation and a higher incidence of arrhythmias during the attack induced by hyperventilation than did the 19 patients with single vessel coronary spasm, and all of them had no significant organic stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Tetraethylammonium-induced contraction of rabbit coronary artery

The vasoactive effect of tetraethylammonium (TEA), a well-known K channel blocker, was tested on helical strips excised from the large epicardial coronary arteries of rabbit hearts. TEA (10 mM) induced transient tetanic contraction of greater amplitude as a result of summation of twitch responses. Occasionally, spontaneous periodic contractions occurred during prolonged exposure to 10 mM TEA. This TEA-induced contraction was abolished in Ca-free solution and suppressed by Ca-entry blockers: nitroglycerin, nicorandil, and isoproterenol, but not by phentolamine or atropine. In strips in which TEA did not induce remarkable contraction, subsequent addition of a subthreshold concentration of ergonovine, serotonin, acetylcholine, ouabain, K-rich solution, or alkalinization of the solution provoked remarkable contraction. These results are consistent with previous reports that TEA induced tetanic contraction as a result of summation of twitch responses due to spontaneous discharge of Ca-spikes in some arterial and tracheal smooth muscle. The results also support the idea that TEA-induced contraction of the rabbit coronary artery is mediated by the same mechanism, i.e., spontaneous Ca-spike discharge.

Vasospastic angina in thyrotoxicosis--case reports

We encountered 2 patients with thyrotoxicosis accompanied at its onset by progressive angina. The ST segment was elevated in one patient and depressed in the other patient during the spontaneous attacks. Coronary arteriographic findings were normal during control, and spasm was induced by ergonovine. No patients had chest pain even without antianginal medication after successful treatment of thyrotoxicosis. The coronary artery may become sensitive to spasm during thyroid hormone excess even in cases without significant coronary artery disease and previous chest pain.

Chest pain and the hyperventilation syndrome--some aetiological considerations

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Variant angina induced by alcohol ingestion

We gave alcohol to 15 patients with variant angina to induce the attacks at the hospital. Anginal attacks were repeatedly induced in seven of them. Although the time lag between alcohol ingestion and the attacks varied widely among patients, from 1.5 to 12 hours, it was fairly constant in each patient. We carefully examined the histories of 101 patients with variant angina to become familiar with the relationship between alcohol ingestion and the attacks of angina. Seventy-one patients took alcohol in their daily lives. Nineteen of the 71 patients (26.8%) who took alcohol had a definite relationship between alcohol ingestion and the attacks. We conclude that alcohol induces anginal attacks or coronary artery spasm in not a small number of patients with variant angina.

Effects of angiographic contrast medium on isolated canine coronary arteries

In isolated canine coronary arteries previously contracted by high potassium concentration, angiographic contrast medium decreased active tension by 61 +/- 2%. The relaxant effect was dose dependent and was not prevented by beta-blockade with d-l-propranolol (10(-5) M). This effect was similar to that obtained with nitroglycerin (10(-6) M), and further relaxation was evident when this vasodilator was administered after exposure to the contrast medium. When arteries were precontracted by alpha-receptor stimulation with norepinephrine (10(-5) M) at normal potassium concentration, a maximal relaxation of 83 +/- 6% was elicited after exposure to contrast medium. The relaxant effect could not be reproduced by a similar increase in osmolarity brought about by addition of sucrose. When arterial strips were processed by radioimmunoassay for dosage of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) after the relaxing action of the contrast medium occurred, a decrease in cAMP from 2.61 +/- 0.86 to 0.63 +/- 0.1 pmol/mg protein (p less than 0.05) was observed, whereas no significant changes in cGMP were detected. These nucleotides do not appear to be involved in the relaxant effect of the dye in the same way as they are when relaxation is elicited by some other coronary vasodilators.