[Tonometry and pachymetry to evaluate fluctuations of intraocular pressure in the context of SCUBA diving]

BACKGROUND

It is currently still not clarified whether diving using a self-contained breathing apparatus (SCUBA) is associated with intraocular pressure (IOP) fluctuations of clinical relevance and whether intensive diving could exacerbate the damage in glaucoma patients.

OBJECTIVE

This study aimed to evaluate the effect of SCUBA diving on IOP in healthy volunteers without prior eye injuries or surgery.

HYPOTHESIS

recreational diving does not lead to significant increases or fluctuations of the IOP.

MATERIAL AND METHODS

The study included 16 divers (5 female) who performed a total of 96 dives with air or nitrox32 to a depth of 20-30 m for an average of 50 min. The central cornea thickness was measured using ultrasonic pachymetry Pocket IITM (Quantel Medical Pocket II™, Quantel Medical, Clermont-Ferrand, France), and the IOP was measured using an Icare® PRO (Icare® PRO, Icare Finland Oy, Espoo, Finland) directly before the dive and 10 min after surfacing.

RESULTS

All data refer to the right eye. Average IOP values ranged from 15.6 to 19.2 mm Hg pre-dive and 16.8 to 18.2 mm Hg post-dive. The range of IOP values was 2.2-11.5 mm Hg pre-dive (∆ = 9.3 mm Hg) and 2.7-14.8 mm Hg post-dive (∆ = 12.1 mm Hg). Of the divers 11.5% vs. 18.8% had increased IOP values > 21 mm Hg (pre-dive vs. post-dive).

CONCLUSION

This study found no significant differences in IOP values between pre-dive and post-dive measurements in healthy SCUBA divers. Therefore, recreational SCUBA diving is unlikely to affect the IOP in healthy individuals.

Reply to Mankowska et al. Comment on "Muth et al. Assessing Critical Flicker Fusion Frequency: Which Confounders? A Narrative Review. Medicina 2023, 59, 800"

First and foremost, we like to express our gratitude for the praise bestowed upon our narrative review [...].

Assessing Critical Flicker Fusion Frequency: Which Confounders? A Narrative Review

The critical flicker fusion frequency (cFFF) refers to the frequency at which a regularly recurring change of light stimuli is perceived as steady. The cFFF threshold is often assessed in clinics to evaluate the temporal characteristics of the visual system, making it a common test for eye diseases. Additionally, it serves as a helpful diagnostic tool for various neurological and internal diseases. In the field of diving/hyperbaric medicine, cFFF has been utilized to determine alertness and cognitive functions. Changes in the cFFF threshold have been linked to the influence of increased respiratory gas partial pressures, although there exist inconsistent results regarding this effect. Moreover, the use of flicker devices has produced mixed outcomes in previous studies. This narrative review aims to explore confounding factors that may affect the accuracy of cFFF threshold measurements, particularly in open-field studies. We identify five broad categories of such factors, including (1) participant characteristics, (2) optical factors, (3) smoking/drug use, (4) environmental aspects, and (5) breathing gases and partial pressures. We also discuss the application of cFFF measurements in the field of diving and hyperbaric medicine. In addition, we provide recommendations for interpreting changes in the cFFF threshold and how they are reported in research studies.

Oxygen-enriched Air Decreases Ventilation during High-intensity Fin-swimming Underwater

Oxygen-enriched air is commonly used in the sport of SCUBA-diving and might affect ventilation and heart rate, but little work exists for applied diving settings. We hypothesized that ventilation is decreased especially during strenuous underwater fin-swimming when using oxygen-enriched air as breathing gas. Ten physically-fit divers (age: 25±4; 5 females; 67±113 open-water dives) performed incremental underwater fin-swimming until exhaustion at 4 m water depth with either normal air or oxygen-enriched air (40% O ₂ ) in a double-blind, randomized within-subject design. Heart rate and ventilation were measured throughout the dive and maximum whole blood lactate samples were determined post-exercise. ANOVAs showed a significant effect for the factor breathing gas (F(1, 9)=7.52; P=0.023; η ²_p =0.455), with a lower ventilation for oxygen-enriched air during fin-swimming velocities of 0.6 m·s ⁻¹ (P=0.032) and 0.8 m·s ⁻¹ (P=0.037). Heart rate, lactate, and time to exhaustion showed no significant differences. These findings indicate decreased ventilation by an elevated oxygen fraction in the breathing gas when fin-swimming in shallow-water submersion with high velocity (>0.5 m·s ⁻¹ ). Applications are within involuntary underwater exercise or rescue scenarios for all dives with limited gas supply.

An Updated Narrative Review on Ergometric Systems Applied to Date in Assessing Divers' Fitness

Many recreational divers suffer medical conditions, potentially jeopardizing their safety. To scale down risks, medical examinations are mandatory and overwhelmingly performed using bicycle ergometry, which overlooks some important aspects of diving. Searching ergometric systems that better address the underwater environment, a systematic literature search was conducted using the keywords 'diving', 'fitness', 'ergometry', and 'exertion'. All presented alternative systems found convincingly describe a greatly reduced underwater physical performance. Thus, if a diver's workload in air should already be limited, he/she will suffer early from fatigue, risking a diving incident. How to assess fitness? Performance diagnostics in sports is always specific for a modality or movement. Therefore, professional scuba divers should be tested when fin-swimming underwater. For the vast number of recreational divers, the current screening can likely not be replaced. However, to prevent accidents, divers need to understand and be able to improve factors that limit their physical performance underwater. Other systems, presented here, will continue to be important tools in underwater research.

Firefighters during training as divers: physiologic and psychomental stresses

Objectives. Fire departments train divers for search, rescue and recovery in and under water. Their tasks likely exert major physical and psychological stress. This study hypothesizes that training is well balanced, following a learning spiral. Methods. Seven firefighters participated, performing 272 dives in different waters. Measurements included pulmonary function (body plethysmography); heart rate (HR) and air consumption during dives; personality variables with the state-trait anxiety inventory (STAI) and psychological stress with the task load index (NASA-TLX). Results. Pulmonary function was maintained at the end of training dives. During the dives, mean HR was 108 ± 23 bpm and mean air consumption 37 ± 15 L/min. Both values remained unchanged during training. The three highest STAI stanines (severe trait anxiety) were not considered, but median stanines and very low values were over-represented. Demands within the seven NASA-TLX areas were perceived differently. Sum of the scales 'very low', 'low' and 'mean' was ≥60%. In turn, the scale 'very high' was in none of the demands >10%. Conclusion. Physiological values remained unaltered throughout training, i.e. workload and increase in competence properly matched. The moderate manifestation of psychomental stress speaks for a group of highly selected individuals. Both candidate selection and design of the learning spiral was successful.

Assessment of a dive incident using heart rate variability

INTRODUCTION

Scuba diving likely has an impact on the autonomic nervous system (ANS). In the course of conducting trials of underwater ECG recording for measurement of heart rate variability, there was an unexpected stressful event; one participant's regulator iced and began to free-flow.

METHODS

A custom-made, water- and pressure-tight aluminum housing was used to protect a portable Holter monitor. ECGs were recorded in three experienced divers who witnessed an unplanned moderately stressful incident during diving. The ECG signals were analysed for measures of heart rate variability (HRV).

RESULTS

Analysis for different short-term HRV measures provided consistent results if periods of interest were appropriately time-aligned. There was improvement in sympatho-vagal balance. One diver unexpectedly exhibited an increase in both sympathetic and vagal activity shortly after the incident.

CONCLUSIONS

A conventional open-water dive affected the ANS of experienced recreational divers as measured by HRV which provides a global evaluation of the ANS and alterations in its two branches. The heart rate variability data gathered from several participating divers around the time of this event illustrate the potential utility of this variable in quantifying stress during diving. HRV data may be useful in addressing relevant diving related questions such as effects of cold, exercise or different breathing gases on ANS function.

Does oxygen-enriched air better than normal air improve sympathovagal balance in recreational divers?An open-water study

Effects of the hyperbaric environment on the autonomic nervous system (ANS) in recreational divers are not firmly settled. Aim of this exploratory study was to (1) assess ANS changes during scuba diving via recordings of electrocardiograms (ECG) and to (2) study whether nitrox40 better improves sympathovagal balance over air. 13 experienced divers (~40yrs) performed two open-water dives each breathing either air or nitrox40 (25m/39min). 3-channel ECGs were recorded using a custom-made underwater Holter-monitor. The underwater Holter system proved to be safe. Air consumption exceeded nitrox40 consumption by 12% (n = 13; p < 0.05). Both air and nitrox40 dives reduced HR (10 vs 13%; p < 0.05). The overall HRV (pNN50: 82 vs 126%; p < 0.05) and its vagal proportion (RMSSD: 33 vs 50%; p < 0.05) increased during the dive. Moreover, low (LF: 61 vs 47%) and high (HF: 71 vs 140%) frequency power were increased (all p < 0.05), decreasing the ratio of LF to HF (22 vs 34%). : Conventional open-water dives distinctly affect the ANS in experienced recreational divers, with sympathetic activation less pronounced than vagal activation thereby improving the sympathovagal balance. Nitrox40 delivered two positive results: nitrox40 consumption was lower than air consumption, and nitrox40 better improved the sympathovagal balance over air.

Effects of Breath-Hold Deep Diving on the Pulmonary System

This short review focuses on pulmonary injury in breath-hold (BH) divers. When practicing their extreme leisure sport, they are exposed to increased pressure on pulmonary gas volumes, hypoxia, and increased partial gas pressures. Increasing ambient pressures do present a serious problem to BH deep divers, because the semi-rigid thorax prevents the deformation required by the Boyle-Mariotte law. As a result, a negative-pressure barotrauma (lung squeeze) with acute hemoptysis is not uncommon. Respiratory maneuvers such as glossopharyngeal insufflation (GI) and glossopharyngeal exsufflation (GE) are practiced to prevent lung squeeze and to permit equalizing the paranasal sinuses and the middle ear. GI not only impairs venous return, thereby provoking hypotension and even fainting, but also produces intrathoracic pressures likely to induce pulmonary barotrauma that is speculated to induce long-term injury. GE, in turn, further increases the already negative intrapulmonary pressure, thereby favoring alveolar collapse (atelectasis). Finally, hypoxia seemingly not only induces brain injury but initiates the opening of intrapulmonary shunts. These pathways are large enough to permit transpulmonary passage of venous N2 bubbles, making stroke-like phenomena in deep BH divers possible.

Sphenoid sinus barotrauma in diving: case series and review of the literature

About 50% of scuba divers have suffered from barotrauma of the ears and about one-third from barotrauma of paranasal sinuses. The sphenoid sinuses are rarely involved. Vital structures, as internal carotid artery and optic nerve, adjoin the sphenoid sinus. Thus, barotrauma could lead to serious neurologic disorders, including blindness. After searching the literature (Medline) and other sources (Internet), we present some cases of sphenoid sinus barotrauma, because these injuries may be underreported and misdiagnosed due to the lack of awareness and knowledge. Therefore, information is provided, e.g. on anatomical and pathophysiological features. Divers and physicians should have in mind that occasional headache during or after diving sometimes signals serious neurological disorders like vision loss. We show that injuries can develop from both negative and positive pressures in the sinuses. Because visual recovery depends on prompt diagnosis and proper therapy, physicians like otolaryngologists, ophthalmologists and neurologists need to closely collaborate.

Anxiety and Depression in Patients Undergoing Mitral Valve Surgery: A Prospective Clinical Study

BACKGROUND

Impending cardiac surgery presents an existential experience that may induce psychological trauma. Moreover, quality of life long after successful coronary artery bypass graft surgery (CABG) can be impaired.

AIM

The aim of this study was to describe the time course of anxiety and depression in patients undergoing mitral valve surgery and compare it with our earlier results of patients undergoing CABG, a disease that is likely to be related to psychosomatic disorders. We hypothesized that patients undergoing mitral valve surgery can better manage stresses of cardiac surgery than patients undergoing CABG.

PATIENTS AND METHODS

Of 117 patients undergoing mitral valve surgery, 100 patients (22 to 87 years; 53 females) completed the study and were interviewed before (pre), 1 week after (early), and 6 months after (late) surgery. The Hospital Anxiety and Depression Scale (HADS) was employed.

RESULTS

The proportion of patients with elevated anxiety scores (AS ≥ 8) was higher than normal (19.8%): pre, 33.0%; early, 28.0%; and was normalized late (18.0%). Similarly, depression scores (DS ≥ 8) were increased: pre, 15.0%; early, 20.0%; and late 14.0%, respectively (normal: 3.2%).

CONCLUSION

Coronary heart disease of CABG patients is presented as a systemic disorder, associated with both higher and postoperatively increased distress levels than in mitral valve patients. Anxiety and depression should be recognized as possible symptoms of psychosomatic disorders necessitating psychotherapeutic intervention to prevent postoperative depression and warrant patient-perceived surgical outcome that is additionally affected by expectations with respect to treatment and individual coping capacities. HADS is recommended to screen for vulnerable patients in the clinical routine, and psychosomatic support should be provided.

"Lung packing" in breath hold-diving: An impressive case of pulmo-cardiac interaction

There is a complex interaction between the heart and the lungs. We report on a healthy female who performs breath hold diving at a high, international level. In order to optimize pressure equalization during diving and to increase oxygen available, apneists employed a special breathing maneuver, so called “lung packing”. Based on cardiac MRI we could demonstrate impressive effects of this maneuver on left ventricular geometry and hemodynamics. Beyond the fact, that our findings support the concept of pulmonary –cardiac interrelationship, it should be emphasized, that the reported, extreme breathing maneuver could have detrimental consequences due to reduction of stroke volume and cardiac output.

Computer-assisted paranasal sinus operation induces diving bradycardia

Unintentional mechanical manipulation anywhere in the distribution of the trigeminal nerve might activate a reflexive bradycardia. Neurosurgeons need to bear in mind detrimental consequences on cardiac function. A female patient (53 years) underwent a computer-assisted (CAS), paranasal sinus operation performed under general anesthesia. During left sided CAS and preparation of the sinus ethmoidalis, heart rate significantly fell from 68 to 32 /min, while systolic arterial blood pressure decreased from 105 to 75 mmHg. Continuation of the preparation again decreased heart rate progressing to transient asystole lasting for 15 s. After removal of the instruments, asystole terminated without medical support. As heart rate decreased after renewed insertion of the CAS probe, sinus ethmoidalis surgery was completed after atropine administration. During neurosurgical procedures, the incidence of the reflex varies between 10 and 18%. To the best of our knowledge, we report for the first time on a direct stimulation of the ethmoidal nerve with instruments (CAS probe) during paranasal surgery. Although normally cardioprotective, exaggeration of the diving reflex can be detrimental and has been implicated in cardiorespiratory disorders, including sudden death and the sudden infant death syndrome.

Physical exercise might influence the risk of oxygen-induced acute neurotoxicity

OBJECTIVE

Hyperoxia can induce acute neurotoxicity with generalized seizures. Hyperoxia-induced reduction in cerebral blood flow velocity (CBFV) might be protective. It is unclear whether dynamic exercise during hyperoxia can overcome CBFV-reduction and thus possibly increase the risk of neurotoxicity.

METHODS

We studied CBFV with both-sided transcranial Doppler with fixed transducer-position and heart rate under increasing hyperoxic conditions in nine professional military oxygen divers. The divers performed dynamic exercise on a bicycle-ergometer in a hyperbaric chamber (ergometries I-III, 21kPa, 100kPa, 150kPa pO2), with continuous blood pressure (ergometries I, II), end-tidal CO2 (PetCO2; ergometry I) being measured.

RESULTS

Systolic (CBFVsyst) and diastolic CBFV (CBFVdiast) readings at rest decreased with increasing pO2. During exercise, CBFVsyst and CBFVdiast significantly increased in parallel with increasing pO2, despite reduced flow velocities at rest.

ERGOMETRY I

CBFVsyst increased from 65.0 +/- 11.3 cm/second at rest to 80.2 +/- 23.4cm/s during maximum workload (n.s.), diastolic from 14.5 +/- 4.1 cm/second to 15.6 +/- 7.5 cm/s (n.s.). PetCO2 increased from 43.4 +/- 7.8mmHg to 50.0 +/- 7.5mmHg.

ERGOMETRY II

CBFVsyst increased from 58.2 +/- 16.5 cm/second to 99.7 +/- 17.0 cm/s (p<0.001), diastolic from 14.0 +/- 10.7 cm/second to 29.4 +/- 11.1 cm/second (p<0.01).

ERGOMETRY III

CBFVsyst increased from 54.4 +/-15.0cm/second to 109.4 +/- 22.3cm/s (p<0.001), diastolic from 14.7 +/- 10.4 cm/second to 35.5 +/- 9.3 cm/second (p<0.01).

INTERPRETATION

Physical exercise overrules the decrease in CBFV during hyperoxia and leads to even higher CBFV-increases with increasing pO2. A tendency towards CO2 retainment with elevated PetCOz may be causative and thus heighten the risk of oxygen-induced neurotoxicity.

Diving reflex: can the time course of heart rate reduction be quantified?

In this meta-analysis of diving bradycardia in humans, we sought to quantify any heart rate (HR) reduction using a relatively simple mathematical function. Using the terms "diving reflex,""diving bradycardia,""diving response,""diving plus heart rate," databases were searched. Data from the studies were fitted using HR=c+aexp(-(t-t(0))/τ), where c is the final HR, a is the HR decrease, τ is the time constant of HR decay, and t(0) is the time delay. Of 890 studies, 220 were given closer scrutiny. Only eight of these provided data obtained under comparable conditions. Apneic facial immersion decreased HR with τ=10.4 s and in air alone it was less pronounced and slower (τ=16.2 s). The exponential function fitted the time course of HR decrease closely (r(2)>0.93). The fit was less adequate for apneic-exercising volunteers. During apnea both with and without face immersion, HR decreases along a monoexponential function with a characteristic time constant. HR decrease during exercise with and without face immersion could not readily be described with a simple function: the parasympathetic reaction was partially offset by some sympathetic activity. Thus, we succeeded in quantifying the early time course of diving bradycardia. It is concluded that the diving reflex is useful to diagnose the integrity of efferent cardiovascular autonomic pathways.

Cardiac stunning in the clinic: the full picture

Cardiac stunning refers to different dysfunctional levels occurring after an episode of acute ischemia, despite blood flow is near normal or normal. The phenomenon was initially identified in animal models, where it has been very well characterized. After being established in the experimental setting, it remained unclear, whether a similar syndrome occurs in humans. In addition, it remained controversial, whether stunning was of any clinical relevance as it is spontaneously reversible. Hence, many studies continue to focus on the properties and mechanisms of stunning, although therapies seem more relevant for attenuating and treating myocardial ischemia/reperfusion (I/R) injury, i.e. to bridge until recovery. This article reviews the different facets of cardiac stunning, i.e. myocardial, vascular/microvascular/endothelial, metabolic, neural/neuronal, and electrical stunning. This review also displays where these facets exist and which clinical relevance they might have. Particular attention is directed to the different therapeutic interventions that the various facets of this I/R-induced cardiac injury might require. A final outlook considers possible alternatives to further reduce the detrimental consequences of brief episodes of ischemia and reperfusion.

Blood pressure and heart rate immediately after termination of short-term ventricular fibrillation

BACKGROUND

Implantable cardioverter/defibrillators (ICDs) can detect ventricular fibrillation (VF) and terminate it. For determining the optimal defibrillation threshold, ventricular fibrillation is repetitively induced and terminated with DC shocks. Depending on the protocol, several fibrillation/defibrillation sequences are mandatory before the final implantation of an ICD. This procedure provides an elegant human model of circulatory arrest and resuscitation.

PATIENTS AND METHODS

In anesthetized 73 patients (15 females) of on the average 60+/-11 years, the end-expiratory pressure was set to zero. Left ventricular pressure (LVP) was monitored with a microtip-catheter, central venous pressure (CVP) through a cannula which was advanced into the superior V. cava. ECG was recorded. After testing, a monoexponential function was found to best fit the time courses of LVP, CVP and heart rate. Data are mean+/-S.D.

RESULTS

After termination of circulatory arrest, peak LVP increased with a time constant tau of 9.2+/-4.2 beats, CVP decreased with tau=2.8+/-1.5 beats, and RR-intervals decreased with tau=4.3+/-3.5 beats. Correlations between prefibrillatory values and steady-state values after termination of fibrillation were high: peak LVP: r=0.78; CVP: r=0.95; RRI: r=0.82.

SUMMARY

After DC termination of VF, the heart 'finds' relatively quickly a steady-state rhythm at the prefibrillatory level (22 beats), thereby normalizing CVP almost in parallel (14 beats). Peak LVP plateaus only after about 40 beats, although reasonable arterial pressures are reached within the first beats. Our data are limited to periods of ventricular fibrillation of no longer than 60s, which limits the generalisability to the setting of clinical cardiac arrest.

Reduction in β-myosin heavy chains in stunned myocardium as assessed by nondenaturing gel electrophoresis

Myosin plays a key role in the structure and function of cardiac muscle. Three myosin isoenzymes (V(1), V(2), and V(3)) with different ATPase activities have been identified in mammalian ventricles based on their heavy chain constituents. The relative amount of myosin isoenzymes changes under physiological and pathological conditions. Until now, myosin isoenzymes have frequently been determined using either tube gel (nondenaturing) polyacrylamide gel electrophoresis (PAGE), or gradient or uniform sodium dodecyl sulfate (denaturing) PAGE. Both methods have disadvantages, e.g., a long running time. We developed, therefore, a uniform, nondenaturing PAGE with slab minigel format for analyzing the myosin isoenzymes in normoxic and stunned rabbit hearts. In normoxic hearts of adult rabbits, V(3) predominated over V(1) (46 vs 41%). In turn, in the stunned hearts, V(1) predominated over V(3) (70 vs 30%), and the heterodimeric V(2) was not anymore detectable. This alteration appears to result from a selective loss of myosin heavy chain (MHC)-beta. In parallel, the biochemical markers troponin I and creatine kinase were increased in the stunned hearts. We suggest that alterations of myosin isoenzymes in stunned myocardium can be monitored with native PAGE. The present analysis of myosin isoenzyme appears thus as a new tool for evaluating defects in MHC dimer formation in postischemic hearts.

Independency of myocardial stunning of endothelial stunning?

BACKGROUND AND OBJECTIVE

Vascular endothelial cells play an important role in the control of vascular tone. The reasons for coronary endothelial dysfunction are complex and may involve ischemia/reperfusion injury. We investigated whether endothelial, smooth muscle, and myocardial dysfunction are independent phenomena.

METHODS

Rabbit hearts were rapidly excised without intermittent ischemia, connected to a modified Langendorff apparatus, and perfused with a modified Krebs-Henseleit solution containing bovine erythrocytes. Normoxic control hearts (n = 16) were perfused for 125 min. Postischemic hearts (n = 15) were perfused for 45 min, submitted to global ischemia (20 min) and reperfused (60 min). Both the normoxic and the postischemic hearts were divided into three groups that received either 0.9% NaCl (placebo), or 3-morpholinosydnonimine (SIN-1; 100 microM),or substance P (SP; 5 nM).

RESULTS

After SIN-1, CBF in the normoxic hearts was increased by maximum 63% and after SP by 62%. 60 min after the onset of reperfusion, the postischemic hearts of both groups had recovered to 95% LVP(max). In the postischemic hearts, SIN-1 increased CBF still by 58%, while the endothelium-dependent vasomotion was impaired: SP improved CBF by only 9%.

SUMMARY AND CONCLUSIONS

The particular protocol permitted differentiation between myocardial and vascular stunning. The results show that, while myocardial function has already recovered, endothelial cells are more severely impaired than smooth muscle cells, and that this injury persists beyond myocardial stunning. Thus, endothelial-dependent dysfunction can still impair vasodilatation while ventricular dysfunction has already resolved.

[Selective I(f) channel inhibition: an alternative for treating coronary artery disease?]

Several clinical studies demonstrate the importance of the heart rate for the cardiovascular morbidity and mortality. Over the last 50 years, some thought has been given to those substances that selectively reduce the heart rate. It is now recognized that I(f) ion channels of the sinus node play a major role in the automatism and modulation of the heart rate. Substances that selectively reduce the heart rate should decrease myocardial oxygen consumption and increase oxygen delivery via the prolonged diastolic coronary perfusion. Direct inotropic effects, however, are unlikely. In principle, anti-anginal and anti-ischemic effects of specific bradycardic substances can be expected. The clinical experience with some of the former bradycardic substances has not been sufficiently convincing. The more recent ivabradine (Procoralan presents an exception to this, as it successfully completed a clinical program for the treatment of chronically stable angina pectoris. In this review article, specific bradycardic substances (= I(f) channel inhibitors) are presented together with the corresponding experimental and clinical studies. The studies were selected against the background of the efficacy of I(f) channel inhibitors in the therapy of cardiovascular disease. As only ivabradine has completed a study on 5,000 patients, the discussion on that particular I(f) channel inhibitor is somewhat extensive. In addition, prospective possibilities and limitations of bradycardic substances are presented.

[Postconditioning: a brief review]

Preconditioning is the most effective form of cardioprotection that can be induced via different interventions before a longer-lasting ischemia (= index ischemia). Preconditioning can be induced by short bouts of ischemia, several pharmaceuticals (e.g., adenosine), and volatile anesthetics. A brief ischemia of an organ other than the heart can likewise initiate protection of the heart, which has been called preconditioning at a distance or remote preconditioning. According to the more recent literature, short bouts of ischemia after an index ischemia can also initiate cardioprotection, e.g., improve postischemic dysfunction or reduce infarct size, which has been called postconditioning. Such a postconditioning can also be elicited at a distant organ, termed remote postconditioning. It is the aim of this short review to characterize preconditioning and in particular postconditioning, describe possible mechanisms, and call attention to the clinical relevance.

Comparison of a beta-blocker and an If current inhibitor in rabbits with myocardial infarction

AIM

We compared protective effects of a ss-adrenoceptor blocker (metoprolol; Met) and a If current (Ivabradine; Iva) in a rabbit model of myocardial infarction.

METHODS

Experiments were performed on 44 adult New-Zealand-White (NZW) rabbits. The effects of either metoprolol or ivabradine were assessed 15 min after experimental occlusion of a coronary artery (CAO), 28 days after CAO (drug gavage), and in vitro hearts (Langendorff apparatus). The results were compared with sham and placebo hearts.

RESULTS

Metoprolol (0.25 mg/kg) slightly reduced heart rate and left ventricular systolic function. Ivabradine (0.25 mg/kg) reduced heart rate significantly (P<0.05) (18% vs control). Both drugs provided advantages over placebo: mortality was significantly (P<0.01)smaller (6/13 Pla animals died, 2/10 Met animals, and 3/11 Iva animals), left ventricular function was better preserved after 28 days (external power; Pla; Met; Iva=56%; 76%; 74%), and dilatation (BNP) was reduced (P<0.05). In the Pla group, the ST segment was significantly (P<0.05) elevated by 0.35 mV after CAO and exhibited in 50% of the animals Q waves after 28 days, while after ivabradine or metoprolol, ST displacement and Q waves had disappeared. The uneconomic myosin isoenzyme V3 predominated in Met hearts and Iva hearts (V3/V1: 63/37% and 62/38%), while it was further increased in Pla hearts (78/21%). External efficiency was lowest in Pla hearts (1.00+/-0.50 a.u.; P<0.05) and was significantly higher both in Met hearts (4.0+/-1.8 a.u.) and in Iva hearts (3.3+/-1.6 a.u.).

CONCLUSIONS

Met and Iva seem suited for the treatment of chronic myocardial infarction.

Delayed preconditioning via Angiotensin-converting enzyme inhibition: pros and cons from an experimental study

1. Bradykinin B(2) receptor activation confers preconditioning from ischaemic injury. In the present study, we tested whether an angiotensin-converting enzyme (ACE) inhibitor (captopril) could mediate delayed preconditioning and, thus, cardioprotection. 2. New Zealand white rabbits received 15 mL infusion of either saline (control group; n = 7) or drugs (0.3 mg/kg captopril (CAP group; n = 7) or 0.3 mg/kg captopril + 0.1 mg/kg HOE 140 (CAPHOE group; n = 7)) via a marginal ear vein over 30 min. After 24 h, hearts were connected to a Langendorff apparatus and buffer perfused. The experimental protocol consisted of 20 min global normothermic hypoxia, followed by 120 min reperfusion. 3. Compared with baseline, the mean (SEM) contractile state (= dP/dt(max)) at 120 min reperfusion was decreased to 42 +/- ;23, 72 +/- ;16 (*P < 0.05 vs control) and 49 +/- ;22% in the control, CAP and CAPHOE groups, respectively. Early relaxation (= dP/dt(min)) was reduced to 55 +/- ;28, 73 +/- ;15 (*P < 0.05 vs control) and 52 +/- ;19% in the control, CAP and CAPHOE groups, respectively. The estimate for myocardial oxygen consumption (MVO(2)= rate-pressure product) was decreased to 52 +/- ;15, 69 +/- ;24 (*P < 0.05 vs control) and 56 +/- ;15% in the control, CAP and CAPHOE groups, respectively. Similarly, coronary flow was decreased in the control, CAP and CAPHOE groups to 49 +/- ;20, 67 +/- ;18 and 46 +/- ;19%, respectively. In contrast, ventricular extrasystoles during reperfusion were significantly elevated in both the CAP and CAPHOE groups (1.3 +/- ;0.2 and 1.1 +/- ;0.3 /min, respectively) compared with control (0.4 +/- ;0.2 /min). 4. Captopril confers delayed preconditioning against stunning via a B(2) receptor-mediated pathway. This pharmacological preconditioning protects against systolic and diastolic stunning, against vascular stunning and preserves cardiac metabolism. In addition to its accepted cardioprotective effects in early preconditioning, captopril should induce delayed preconditioning (e.g. for routine interventional cardiology or in elective cardiac surgery).

Decompression Sickness Following Breath-hold Diving

Despite convincing evidence of a relationship between breath-hold diving and decompression sickness (DCS), the causal connection is only slowly being accepted. Only the more recent textbooks have acknowledged the risks of repetitive breath-hold diving. We compare four groups of breath-hold divers: (1) Japanese and Korean amas and other divers from the Pacific area, (2) instructors at naval training facilities, (3) spear fishers, and (4) free-dive athletes. While the number of amas is likely decreasing, and Scandinavian Navy training facilities recorded only a few accidents, the number of spear fishers suffering accidents is on the rise, in particular during championships or using scooters. Finally, national and international associations (e.g., International Association of Free Drives [IAFD] or Association Internationale pour Le Developpment De L'Apnee [AIDA]) promote free-diving championships including deep diving categories such as constant weight, variable weight, and no limit. A number of free-diving athletes, training for or participating in competitions, are increasingly accident prone as the world record is presently set at a depth of 171 m. This review presents data found after searching Medline and ISI Web of Science and using appropriate Internet search engines (e.g., Google). We report some 90 cases in which DCS occurred after repetitive breath-hold dives. Even today, the risk of suffering from DCS after repetitive breath-hold diving is often not acknowledged. We strongly suggest that breath-hold divers and their advisors and physicians be made aware of the possibility of DCS and of the appropriate therapeutic measures to be taken when DCS is suspected. Because the risk of suffering from DCS increases depending on depth, bottom time, rate of ascent, and duration of surface intervals, some approaches to assess the risks are presented. Regrettably, none of these approaches is widely accepted. We propose therefore the development of easily manageable algorithms for the prevention of those avoidable accidents.

Gene expression in acute Stanford type A dissection: a comparative microarray study

Background

We compared gene expression profiles in acutely dissected aorta with those in normal control aorta.

Materials and methods

Ascending aorta specimen from patients with an acute Stanford A-dissection were taken during surgery and compared with those from normal ascending aorta from multiorgan donors using the BD Atlas™ Human1.2 Array I, BD Atlas™ Human Cardiovascular Array and the Affymetrix HG-U133A GeneChip^®. For analysis only genes with strong signals of more than 70 percent of the mean signal of all spots on the array were accepted as being expressed. Quantitative real-time polymerase chain reaction (RT-PCR) was used to confirm regulation of expression of a subset of 24 genes known to be involved in aortic structure and function.

Results

According to our definition expression profiling of aorta tissue specimens revealed an expression of 19.1% to 23.5% of the genes listed on the arrays. Of those 15.7% to 28.9% were differently expressed in dissected and control aorta specimens. Several genes that encode for extracellular matrix components such as collagen IV α2 and -α5, collagen VI α3, collagen XIV α1, collagen XVIII α1 and elastin were down-regulated in aortic dissection, whereas levels of matrix metalloproteinases-11, -14 and -19 were increased. Some genes coding for cell to cell adhesion, cell to matrix signaling (e.g., polycystin1 and -2), cytoskeleton, as well as several myofibrillar genes (e.g., α-actinin, tropomyosin, gelsolin) were found to be down-regulated. Not surprisingly, some genes associated with chronic inflammation such as interleukin -2, -6 and -8, were up-regulated in dissection.

Conclusion

Our results demonstrate the complexity of the dissecting process on a molecular level. Genes coding for the integrity and strength of the aortic wall were down-regulated whereas components of inflammatory response were up-regulated. Altered patterns of gene expression indicate a pre-existing structural failure, which is probably a consequence of insufficient remodeling of the aortic wall resulting in further aortic dissection.

Forty years of glucose-insulin-potassium (GIK) in cardiac surgery: a review of randomized, controlled trials

Glucose-insulin-potassium (GIK) solutions have been used in cardiac surgery for more than 40 years. At that time, membrane-polarizing and stabilizing effects on cardiomyocyte's action potential were regarded the main benefit. Two meta-analyses described methodological flaws in the early studies (e.g., case numbers, randomization principles, and levels of significance), and came to clearly different recommendations with regard to the usage of GIK in the therapy of acute myocardial function. During the 70s, as promising therapies for the treatment of AMI had become available (e.g., beta-blockers and thrombolytic agents), the GIK technique was more widely introduced in cardiac surgery, e.g., during valve replacement. At present, 74 of 91 studies provide convincing evidence for the beneficial effects of insulin and/or GIK in cardiac surgery that go far beyond simple metabolic benefits and also include better recovery of myocardial tissue after ischemia. Yet, the exact underlying mechanisms remain still unknown. In this review article, two questions will be answered: why did GIK not become daily routine in cardiac surgery in spite of positive results from clinical studies, and does this technique merit more acceptance among the potential users? In view of the increasing number of older patients at higher risk, the demand for improving surgical procedures has renewed the interest in the GIK concept. The more recent literature suggests that the entire potential of GIK solutions has not been fully disclosed. A large single or multicenter trial with sound endpoints is mandatory.

Resting pulmonary ventilation in sports scuba divers

It should be investigated whether the traditional dependency between respiratory and systemic measures is preserved during scuba diving, and whether the diving experience would affect respiration. Additionally, respiration data were analyzed for gender differences (118 sports divers). Respiratory variables were assessed at poolside and during diving in the pool. The respiration pattern at poolside was significantly different from the pattern during diving, where respiration rate (RR) decreased (11.8 +/- 3.8 vs. 7.8 +/- 2.9 min(-1); -34%) and tidal volume increased (1.1 +/- 0.5 vs. 1.6 +/- 0.6 L; +45%). This produced a decrease in respiratory minute volume (RMV) from 12.4 +/- 4.7 to 11.2 +/- 3.8 L/min (-10%). Respiratory Minute Volume and vital capacity correlated at poolside. This physiologic correlation was lost while diving. Instead, RMV and number of dives (= diver's experience) correlated negatively. Because RMV at both poolside and during diving correlates with RR, an increased RMV in diving beginners can be estimated via RR. Thus, close observation of RR could help improve safety during a regular dive, avoiding hazardous hyperventilation. Female divers, irrespective of body height and weight, need less air during diving.

Ventricular constraint in dilated cardiomyopathy: a new, compliant textile mesh exerts prophylactic and therapeutic properties

BACKGROUND

Dilated cardiomyopathy is associated with a progressive decrease in cardiac function, leading to end-stage heart failure. We aimed to stop this process by mechanically constraining the heart with a new, compliant textile mesh.

METHODS

In 16 male Munich minipigs (50 +/- 7 kg), dilated cardiomyopathy with congestive heart failure was induced through 4 weeks of rapid ventricular pacing (220 beats/min). In the early-mesh group (n = 8), a polyvinylidene fluoride mesh was positioned around both ventricles before pacing was started. In the other group (n = 8), experimental dilated cardiomyopathy through rapid pacing was induced (no mesh). After mesh grafting, rapid pacing was continued (late mesh).

RESULTS

Rapid pacing in the no-mesh group (control group) significantly decreased both systolic (cardiac output, peak systolic pressure, and the derivative of pressure increase [dP/dt(max)]) and diastolic (minimum rate of pressure rise [dP/dt(min)] and left ventricular end-diastolic pressure) variables, whereas these variables remained almost unchanged in the early-mesh group. In the late-mesh group the passive-elastic constraint not only prevented further deterioration but even exerted reverse remodeling to some extent (dP/dt(max) and left ventricular end-diastolic pressure, P < .05).

CONCLUSIONS

Ventricular constraint with the new mesh seems to be a prophylactic and therapeutic option in cardiac insufficiency caused by ventricular dilation. This passive-elastic cardioplasty induced reverse remodeling of dilated hearts and significantly improved diastolic and systolic ventricular function.

Does adenosine pharmacologically precondition human myocardium during coronary bypass surgery?

AIM

Adenosine (Ado) triggers ischemic preconditioning. We investigated whether Ado provides additional myocardial protection in patients during intermittent aortic cross-clamping (IAC) bypass surgery.

METHODS

The placebo group was made of 15 male of 66+/-8 years while the Ado group was made of 19 male of 65+/-10 years. The patients of the Ado group had a 3-vessel heart disease and were treated with elective surgery. With the aortic cross-clamping, Ado or vehicle were infused over 10 min at systemic pressure together with sufficient blood via the aortic root. Blood samples before anaesthesia and onset of ECC, 1 hour after end of surgery, and on day 1 and 2 post-surgery to assess CK-MB and troponin I were performed. Hemodynamic measures (heart rate, left ventricular pressure, max/min pressure rise, central venous pressure) before installation and 15 min after completion of the coronary artery bypass. Different ECGs for electrophysiological analyses were performed.

RESULTS

Hemodynamic and laboratory measures revealed no significant advantages of either protocol. Mortality rate was zero in both groups.

CONCLUSIONS

The comparable outcome is likely due to cardioprotection provided by both IAC bypass surgery and hypothermia, which might obscure beneficial effects of pharmacological preconditioning in patients with good left ventricular function (ejection fraction >50%). As the benefit might have been marginal, it may well become apparent in a larger study on patients with more severe left ventricular dysfunction.

Evidence for palliative enlargement of the right ventricular outflow tract in severe tetralogy of Fallot

OBJECTIVE

If the pulmonary artery (PA) tree in patients with Fallot's tetralogy (TOF) is extremely hypoplastic, a shunt procedure may be difficult and not desirable because of side-effects. Moreover, the failing catch-up growth of the pulmonary annulus is well known. In patients with a severe form of TOF, we performed palliative transannular patching of the right ventricular outflow tract. The early and long-term follow-up was evaluated.

METHODS

Eleven patients (93 days (10-245 days); 3.5+/-0.7 kg (2.5-4.3 kg)) had highly symptomatic TOF (Hb: 18+/-2g/dl, SO2: 68+/-11%); angiographic diameters: RPA: 4.1 mm (2.5-6.4 mm), LPA: 3.4 mm (1.6-7.0 mm), PA trunc: 4.4 mm (2.5-7.0 mm). All 11 underwent transannular enlargement of the right ventricular outflow tract without closure of the ventricular septum defect. A PA index (cross-sectional area of the pulmonary arteries to BSA) was used to compare pre- and postoperative data. For follow-up, the patients were repetitively examined clinically and echocardiographically.

RESULTS

Preoperative PA index was 87+/-40 mm2/m2 (normal: 330+/-35 mm2/m2). Postpalliation angiograms (age: 10-14 months) demonstrated a significant catch-up growth in nine patients (PA index from 99+/-40 to 310+/-54 mm2/m2) and inadequate growth in two patients (PA index 63 and 115 mm2/m2). Perioperative mortality was zero. Ten patients (43 months; 6-105 months) underwent elective repair. Six patients received pulmonary homograft valves (6-15 years after repair) because of severe pulmonary valve insufficiency and severe RV dilation.

COMPLICATIONS

One patient died 10 months postpalliation due to pneumonia, one patient received a pacemaker after repair and died (2 months post-repair) due to pacemaker failure, a 5-year-old patient died 1 month after repair due to sepsis. All eight long-term survivors (12-17 years) are in excellent clinical condition. Echocardiography revealed good RV function and near normal diameters at peak systolic pressures between 25 and 50 mmHg. Only one patient developed brady-arrhythmia; a pacemaker was implanted 8 years after repair and 2 years after homograft implantation.

CONCLUSIONS

In a very severe form of TOF, palliative right ventricular outflow tract construction may provide the potential for complete repair. In the presented high-risk patient group, mortality was not related to the hypoplastic pulmonary arteries. Obviously, all patients need pulmonary valve implantation in the long run.

Intermittent aortic cross-clamping for coronary artery bypass grafting: a review of a safe, fast, simple, and successful technique

Since the very beginning of coronary artery bypass grafting, the search for optimal myocardial protection has fascinated both clinicians and basic researchers. This retrospective review of a large patient cohort aims to display the advantages of one of the protective procedures, namely simple, intermittent aortic cross-clamping (IAC). Thus, this review aims to significantly contribute to daily bypass surgery. This review reports on coronary patients who were all operated on in international centers using IAC such that this review presents the state of the art on IAC. In addition, this review reports on the usage of IAC for more than 2 decades in the clinic of Dr. Bircks, Duesseldorf (DE) and the clinics of his former students. A meta-analysis of published data of international centers summarizes 7 837 operated patients with a total mortality of 123 (=1.6%). This excellent outcome compares well to the results of the Bircks'-related centers, where between 1978 and 2001, a total of 41 573 patients were revascularized with the help of IAC according to the original protocol. The total mortality was 778 (1.9%), with the lowest mortality rate (1.2%) in the largest center (Bad Oeynhausen, DE). According to the presented experience, IAC for coronary revascularization proves to be a highly effective method for myocardial protection; it has convincingly proven to be simple, safe and cost-efficient.