PHOTO COURTESY OF NEIL VINCENT. 32 IMMERSED, SPRING 2001 The International Technical Diving Magazine

Transcription

1 Divin PHOTO COURTESY OF NEIL VINCENT 32 IMMERSED, SPRING 2001 The International Technical Diving Magazine

2 g With Heart a Broken By Barbara L. Krooss, Ph.D. As many as one in three people has a heart condition at birth that cold make them more ssceptible to potentially life-threatening decompression sickness, sometimes after years of problem-free diving. Exertion, inclding an overly forcefl se of the most commonly taght method to eqalize middle ear pressre, can increase the likelihood of problems, even while the body is otgassing after a dive. The condition is a heart defect called patent foramen ovale, or PFO. This mothfl of Latin means a patent or evident, foramen or small opening that is oval. This oval flaplike opening is in the interatrial septm, the tisse between the atria, two of the for chambers of the heart. Everyone has this open hole in the heart before birth when it is needed so fetal circlation can bypass the lngs. A baby s first breath shold case pressre in the left atrim to increase, so that the flap covering this opening closes and it normally eventally seals. Yet this valve flap stays loose in some persons, casing an atrial septal defect or interatrial shnt called PFO. Estimates of PFO among adlts vary from 10 percent to 30 percent. The variation can be attribted to differences in the sensitivity of varios diagnostic techniqes, becase some PFOs may be forced open only nder extreme stress. The incidence of PFO generally is clinically insignificant, since the pressre in the left side of the heart is generally greater than in the right, keeping the flap closed. Diagnostic testing for PFO involves monitoring blood flow dring several repetitions of actions likely to force open the hole. A PFO may be rather large p to 0.18 of a sqare inch / 120 sqare millimeters or consist of a nmber of small openings. A PFO may not always be open, bt a sdden strain and its rebond effects cold case a previ- The International Technical Diving Magazine IMMERSED, SPRING

3 NORMAL HEART AND PFO HEART To Right Lng Plmonary Artery Aorta Normal Heart Bbbles enter the right atrim, To Left Lng pass to the right ventricle, and then travel to the lngs throgh Plmonary Veins the plmanary artery. (from Lngs) Heart with Patent Foramen Ovale Bbbles travel to the lngs as before, bt they also psh throgh the foramen ovale. Bbbles now in the left atrim, pass to the left ventricle and travel throgh the aorta to varios body tisses and possibly even the brain. To Brain, Body Tisses ILLUSTRATION: HOFFMANN & TUNG osly closed bt lightly fsed opening to tear open. This cold accont for injries attribted to heart attacks and strokes in older divers, who previosly had not experienced problems bt who, becase of loss of physical conditioning, now mst se more effort to perform once-easy tasks. Actions that case the pressre in the right atrim to be greater than that in the left can open the flap. These can inclde pressre releases following activities casing isometric tension, sch as coghing, lifting or a forcefl Valsalva manever. Named for Antonio-Maria Valsalva, a 17th-centry Italian anatomist, this commonly taght action increases pressre in the chest by breath-holding while bearing down against the diaphragm. Divers generally se a very gentle form of the Valsalva manever to introdce air into the estachian tbes to eqalize pressre in the middle ear, bt more forcefl versions may be experienced while lifting, especially while holding one s breath, or when defecating. The release of a Valsalva manever cases a decrease in pressre of the airway and chest cavity. This is followed by a sdden increase in blood retrning to the right atrim of the heart and by an increase in the venos blood filling of the lngs, with a resltant decrease in flow to the left heart. The blood shift reslting from the increase in chest cavity pressre cases a rise in the right atrial pressre and a leftward blging of the interatrial septm for the next few heartbeats, which cold open a PFO. This can be dangeros becase bbbles cold then pass into the coronary arteries, restricting blood spply to the heart and distrbing the rhythmic pmping or possibly even damaging the heart mscle. PFO and DCS Dring normal decompression, nitrogen is otgassed from peripheral tisses into the bloodstream. The lngs filter ot gas bbbles in blood retrning throgh the veins before they can reach the brain. However, if bbbles are able to leak from the right side of the heart to the left and thereby enter into the arterial circlation, they can lodge in the brain, casing dangeros nerological decompression sickness hits. Given the high prevalence of PFO and the low incidence of DCS, it s easy to conclde that it s not generally a problem. Yet PFO may be the clprit when DCS hits early and hard, as in nerological symptoms and in ndeserved hits taken by those who have violated no known diving rles. According to the British SbAqa Clb, between 30 percent and 50 percent of all cases of DCS involve ndeserved hits. Evidence sggests that size matters in PFOs. P. Germonpre s grop at the Centre for Hyperbaric Oxygen Therapy at the Military Hospital, Brssels, Belgim, compared 37 divers who sffered nerological DCS with a matched control grop of divers who never had DCS. The grop sed transesophageal contrast echocardiography to estimate PFO size. They conclded that PFO plays a significant role in nexplained cerebral DCS, bt not of spinal DCS. Their stdy, pblished in 1998, reported that divers with DCS with lesions localized in the high cervical spinal cord, inner ear, or cerebellm or cerebrm of the brain had a significantly higher prevalence of PFO than did divers with DCS in the lower spinal cord. In nexplained DCS, this difference was significant only among those with large PFOs. P.T. Wilmshrst s grop at the Department of Cardiology, St. Thomas s Hospital, London, stdied 61 divers with decompression sickness, 47 percent of whom had received ndeserved hits. Most of these divers had PFO. In addition, divers whose DCS symptoms began more that 30 mintes after srfacing or who had joint pain only, actally had fewer right-to-left shnts, or PFOs, than did a control grop of divers withot DCS: 17 percent verss 24 percent. Yet, 34 IMMERSED, SPRING 2001 The International Technical Diving Magazine

4 PFO may be the clprit when DCS hits early and hard, as in nerological symptoms, and in ndeserved hits taken by those who have violated no known diving rles. divers whose nerological symptoms began within 30 mintes of srfacing were 65 percent more likely to have PFO. In addition, they fond that rashes soon after srfacing were related to shnts [PFOs] bt late rashes were not. Nerological Damage J. Rel pset the diving commnity in 1995 with a report pblished in the British medical jornal Lancet that stated that divers were more likely to have brain lesions than wold a normal control grop. Wilmshrst s stdy frther fond that the prevalence of mltiple brain lesions in divers paralleled the prevalence of PFO, and he theorized that divers with PFO wold have a higher risk of developing brain lesions. Follow-p research in a stdy led by M. Knath in 1997 spported the view that PFO places divers at mch greater risk for brain lesions. Knath s grop at the Department of Neroradiology, University of Heidelberg, Germany, sed transcranial Doppler imaging to stdy the brains of 87 sport divers with and withot PFO who had at least 160 dives each. They conclded that mltiple brain lesions in sport divers were associated with the presence of a large patent foramen ovale. Of the 25 divers with PFOs, 13 had ones with sbstantial effect on blood movement. Forty-one brain lesions were detected in 11 divers. Only seven lesions were fond in the 62 divers withot PFO. The remaining 34 lesions were fond in the 25 divers with PFO. Mltiple brain lesions occrred exclsively in three divers with large PFOs. Apparently, the smaller the PFO, the less the risk of brain lesion. Knath s grop fond fewer brain lesions in divers than did Rel s earlier stdy. More than half of Rel s divers had at least one brain lesion, while only 13 percent of Knath s diving grop had brain lesions. The greater nmber of lesions in Rel s grop may be the reslt of differences in measrement technology and definition of lesion. Regardless, those who do extensive decompression diving, especially in conditions involving physical exertion dring otgassing, might want to know whether they have a large PFO. Detecting PFO in Divers Three methods are sed to diagnose PFO. All procedres se 0.2 to 0.3 flid onces / 6 to 8 milliliters of a contrast soltion of agitated saline that contains air bbbles. This bbbly soltion is injected into a vein dring normal respiration and in conjnction with some repetitive action sch as a cogh or performing a Valsalva manever, which shold open the PFO flap. Blood flow following injections is compared dring the flap-opening manever verss the resting condition. Three-dimensional transesophageal echocardiography, or TEE, is the most sensitive of measrement methods, bt the most ncomfortably invasive since a probe is placed in the back of the throat, which mst be anesthetized for optimal imaging of the interatrial septm. Bbble contrast transthoracic echocardiography, or TTE, ses electronic imaging measre across the chest; while transcranial Doppler, or TCD, the least sensitive of the three, ses a sonographic imaging from the of the right middle cerebral artery in the head. E.K. Kert s grop at Loisiana State University Medical Center, New Orleans, compared the three diagnostic methods in 26 divers with nerological DCS symptoms verss 30 normal control sbjects. No difference was seen between the bent divers and the control sbjects at rest. However, when a Valsalva manever was performed, the differences in detecting PFO became apparent. Srprisingly, TCD sonography, the least senstive method, was fond to be the best predictor of nerological DCS risk in divers. Kert s researchers conclded that it is KINDER, GENTLER WAYS TO EQUALIZE The Valsalva manever, the method divers are commonly taght to relieve middle air pressre, can lead to decompression sickness among persons with patent foramen ovale, especially when it is sed forceflly to clear the ears on second dives while the body is still offgassing from a first dive. Fortnately, there are alternate methods that are less likely to case problems. Toynebe manever: Swallow while the moth and nose are closed, which pshes air into the estachian tbes and relieves middle ear pressre. Frenzel manever: Move the moth mscles forward and side-toside to open the estachian tbes, then se the tonge as a piston to psh air into the middle ear. The Valsalva manever entails pshing pward on with the diaphragm while the nasal passages are closed to eqalize pressre in the middle ear. When gently performed this cases no problems. However, more forcefl versions may be experienced while lifting, especially while holding one s breath or when defecating. The release of a Valsalva manever cases a decrease in pressre of the airway and chest cavity. This is followed by a sdden increase in blood retrning to the right atrim of the heart and by an increase in the venos blood filling of the lngs, with a resltant decrease in flow to the left heart. The blood shift reslting from the increase in chest cavity pressre cases a rise in the right atrial pressre and a leftward blging of the interatrial septm for the next few heartbeats, which cold open a PFO. This can be dangeros becase bbbles cold then pass into the coronary arteries, restricting blood spply to the heart and distrbing its rhythmic pmping or possibly even damaging the heart mscle. The International Technical Diving Magazine IMMERSED, SPRING

5 likely that transcranial Doppler identified only larger right to left shnts [PFOs], so this less sensitive method is actally a more effective tool for detecting meaningfl PFO in divers, becase only large PFOs seem to be implicated in decompression sickness. The smaller leaks detected by the other methods do not seem to be meaningfl in DCS risk. This research appears to confirm the folk wisdom that cations against being overly sensitive when dealing with a broken heart. Mending Broken Hearts The good news is that not only can PFO be repaired, bt that the treatment is becoming safer as well. Instead of invasive cardioplmonary bypass srgery, repairs are made by inserting a plg in the hole. The Amplatzer septal occlder plg made by the AGA Medical Corp., Golden Valley, Minn., crrently is the treatment of choice. K.P. Walsh s grop reported in the *American Jornal of Cardiology* in 1999 that AGA s device had a higher rate of closing PFOs and took less floroscopy time. AGA s device took only 13 mintes of X-rays, compared with the 24 mintes needed to insert the Sideris adjstable bttoned device, a plg made by Cstom Medical Devices, Athens, Greece. There may be some dobt abot this comparison, however, even thogh the same team did all of the srgeries. The Sideris plgs were implanted between September 1993 and Febrary 1996, and the Amplatzer devices between December 1996 and March Increased experience by the srgical team might accont for the difference. F. Berger s researchers at the Klinik fr Angeborene Herzfehler, Detsches Herzzentrm Berlin, Germany, reported the reslts of implanting Amplatzer devices in Of the 200 patients stdied, 98.1 percent had complete closre, and a fnctionally trivial amont of shnting in the remainder throghot 1,898 patient-months, or a follow p of 9.5 months per patient. Walsh s grop at Alder Hey Children s Hospital, Liverpool, England, reported in 1999 on the Amplatzer devices sed to sccessflly repair PFOs in seven divers, aged 18 to 60, who had experienced nerological DCS. Follow-p contract echocardiography showed that leakage was flly eliminated in six of the divers, while one still leaked a few bbbles. All patients have received medical clearance to resme diving. PFO repairs can be made even safer, according to a report pblished last Febrary by P. Ewert s researchers at Bteilng Fr Angeborene Herzfehler, Detsches Herzzentrm Berlin, Germany. Walsh s grop fond that implanting Amplatzer devices reqired an average of 14 mintes of X-ray exposre. In many cases, this exposre can be avoided, according to Ewert. Echocardiography provided sfficient gidance to position implants in 19 of 22 cases, with no increase in srgery time. However, sing sond waves to position the devices reqired significantly more sedation of the patient. Safety Sggestions Divers with histories of ndeserved hits or divers who tend to develop a skin rash dring the earlier stages of otgassing are at greater risk. Divers, especially those with PFO, are cationed by C. Balestra s researchers to avoid strenos leg, arm or abdominal exercise after decompression dives. Sch activities cold case a rise and fall in chest cavity pressre sfficient to case a rebond blood loading to the right atrim of the heart. This rebond cold increase the possibility of PFO leaks that cold case paradoxical nitrogen gas bbbles. In 1998, Balestra s grop reported research done at the Laboratory of General Biology in the Universite Libre de Brxelles, Belgim, comparing varios activities that cold significantly change chest cavity pressre. Those most likely to open a PFO inclded breath-hold knee bends, a 172 percent increase; coghing, 133 percent; and maximal Valsalva manever, 136 percent. However, a gentle Valsalva manever, as sed for normal ear-clearing, did not prodce a significant post-release shift in blood flow. Balestra s grop notes that PFOs have been fond in divers strck with ndeserved hits after over 1,000 safe dives, and hypothesizes that exertion in older divers cold case a previosly closed, bt only lightly fsed, PFO may become largely patent over time. They said that in some persons, the shape of the interatrial septm might not permit a rightto-left shnt in normal circmstances bt allow a massive shnt if the diving pressre is sfficiently high. They added that several older and more experienced divers have been strck by repeated episodes of nexplained decompression illness after having sometimes performed more than 1,000 dives withot any problems. In all of these divers, on TEE, a large PFO was detected. Balestra s grop conclded that divers with PFO shold not to perform any forcefl Valsalva manevers that case a real rise in chest cavity pressre immediately after ascent becase silent bbbles can be present in the central venos blood for two hors after a deep dive. They also advised that otgassing divers shold not perform sstained isometric exercise or abdominal strains, sch as defecating, lifting diving tanks or orally inflating a boyancy device at the srface. Another important implication for diving instrctors is that stdents shold be taght to avoid performing forcefl Valsalva manevers. Instead, sing Frenzel or Toynbee manevers, which employ only jaw and throat mscles, shold be given special attention in classes. Althogh post-dive Valsalva manevers wold be more likely to occr in the head of the dive boat, rather than to eqalize pressre in the head of the diver. Forcefl ear clearing while descending again after a one-hor srface interval cold place a diver at risk as well. Barbara Krooss, Ph.D., clinical neropsychology, is an instrctor with NAUI and the Handicapped Scba Association. Her previos articles in Immersed were on injry statistics (Spring 2000), hypothermia (Smmer 1999), oxygen s vale in beating the bends (Winter 1998) and diving and drgs (Winter 1997). Article from Spring 2001 isse of Immersed magazine Order available back isses at 36 IMMERSED, SPRING 2001 The International Technical Diving Magazine