Chapter 24: HPNS

Davy's hands started shaking on day fourteen.

It began during breakfast — the slight tremor in the fingers as he lifted his mug of tea, the liquid shivering in the cup, the surface of the tea describing small concentric circles that Kwame noticed the way he noticed a change in current at depth, not by looking for it but by the peripheral awareness of a man whose attention was calibrated by twelve years of working in an environment where small changes signified large consequences.

The tremor was fine — not the gross shaking of cold or fear but the micro-vibration of a nervous system under pressure, the neural pathways firing with a frequency that the body could not entirely suppress. Kwame recognised it. He had seen it before, in other divers, in himself during his early rotations, the phenomenon that the medical literature called High Pressure Nervous Syndrome and that the divers called, when they called it anything, the shakes.

HPNS was the body's protest against the depth. The mechanism was not fully understood — the research suggested that the high partial pressure of helium affected the cell membranes of the neurons, altering their excitability, increasing the rate of spontaneous firing, the nervous system becoming, at depth, slightly too sensitive, slightly too reactive, the signals that travelled the neural pathways arriving with a tremor that the muscles faithfully reproduced. The effect varied with the individual — some divers experienced nothing, their nervous systems tolerating the pressure with the indifference of a system designed for a wider range than most. Some experienced the tremor. Some experienced nausea. Some experienced both, and the both was the worst, the body shaking and the stomach heaving simultaneously, the two symptoms feeding each other in a loop that could, if not managed, escalate from discomfort to incapacitation.

Davy was twenty-eight. This was his sixth rotation. On his previous rotations, the HPNS had been minimal — a slight unsteadiness in the hands during the first week, subsiding as the body adapted, the nervous system recalibrating to the depth the way the ears recalibrated to the helium voices, the adjustment period a few days and then the symptoms resolved and the body functioned within its new parameters.

This rotation was different. The tremor at fourteen days was late — later than the initial adaptation period, later than the window in which HPNS typically presented. A tremor at fourteen days was not the body adjusting. It was the body accumulating, the cumulative effect of two weeks at 15.2 bar building in the neural tissue, the pressure working on the cell membranes with the slow persistence of a force that did not diminish with time, the helium pressing against the lipid bilayers of the neurons, the structure flexing under the sustained load.

Kwame watched Davy eat. The tea reached Davy's mouth without spilling, the tremor controlled by the effort of concentration, the young diver managing the symptom the way a pilot managed turbulence — by gripping harder, by focusing, by applying conscious control to a process that should have been automatic. The effort was visible in Davy's face — the set of the jaw, the narrowing of the eyes, the attention directed at the simple act of drinking tea as though it were a procedure requiring a checklist and a permit.

Sean was talking. Sean's voice, in the helium register, described a fishing trip that may or may not have occurred, the narrative's relationship to reality being, by this point in the rotation, a matter of faith rather than evidence. Tomasz was doing his crossword. Mac was reading — page 156, the novel's progress as glacial and as certain as the decompression schedule. Fraser was cleaning something that did not need to be cleaned.

Nobody mentioned Davy's hands. The chamber's code applied. A man's symptoms were his own business unless they affected the safety of the dive, and a tremor at breakfast, while notable, was not a safety concern. A tremor at breakfast was a medical fact, a physiological data point, a thing to be observed and monitored and, if it worsened, reported to the dive superintendent, who would consult with the diving physician, who would assess the diver's fitness to continue, who would make a decision based on the data and the examination and the particular calculus of risk that governed the industry's management of the human body at depth.

Kwame reported it anyway. Not to the dive superintendent — that was a step he would not take without Davy's knowledge, the unwritten rule of the chamber's social contract being that you did not report a man's condition behind his back unless the condition was an immediate danger to the team. He reported it to Sarah Webb, on the intercom, during the next atmospheric reading, the words embedded in the routine exchange of numbers.

Sarah, he said. PPO2 and CO2 are reading normal in here.

Sarah's voice came back, calm, precise. Confirmed. PPO2 zero-point-four bar. CO2 zero-point-three per cent. Temperature twenty-nine degrees. All parameters nominal.

Kwame said: Davy is showing some tremor. Hands. Noticed it at breakfast. No other symptoms reported.

The line was quiet for a moment. Sarah understood the communication — the information delivered within the routine, the observation placed alongside the atmospheric data, the human parameter reported with the same neutrality as the gas parameters. The delivery was deliberate. The other men in the chamber could hear the intercom, and Kwame had framed the observation as a report rather than a concern, the difference in tone the difference between noting a fact and raising an alarm.

Sarah said: Copied. I will note it in the medical log and inform the superintendent. We will monitor. Please advise if symptoms change.

Kwame acknowledged. He went to his bunk. He opened his Achebe and did not read it. He held the book and thought about Davy, who was lying in his own bunk three metres away, who was lying very still, who was holding his hands flat against his thighs, the stillness a form of monitoring — the diver watching his own body the way Sarah watched the gauges, checking the parameters, assessing the state, looking for the change that would indicate a worsening.

Davy said: I know you noticed.

Kwame lowered the book. He looked at Davy across the chamber.

Davy said: The shakes. It started this morning. It's in the hands. Nowhere else. No nausea. No headache. Just the hands.

Kwame said: I had it on my third rotation. Both hands. And my jaw — the muscles would twitch, right here. He touched the hinge of his jaw. Three days, and it passed. The body adjusted. The body always adjusted.

This was not entirely true. The body usually adjusted. The body adjusted in the majority of cases, the HPNS resolving as the nervous system found its accommodation with the pressure, the cell membranes stabilising, the tremor fading. But in some cases the body did not adjust, and the diver was extracted from the rotation — decompressed early, brought to the surface, the career not ended but interrupted, the body's refusal to tolerate the depth a fact that had to be respected because respecting it was the difference between a diver who returned next rotation and a diver who did not return at all.

Davy said: What if it doesn't pass?

Kwame said: Then you talk to Gary. Gary has seen it. Gary has been there himself — he had HPNS on three of his early rotations, and he did twenty years in sat. He will not think less of you. Nobody will think less of you.

Davy was quiet. The chamber hummed. The ventilation moved the heliox through the system, the same gas that was dissolving into Davy's neural tissue at the molecular level, the same helium that was pressing against the cell membranes of his motor neurons and producing the tremor that Davy was trying not to think about and could not stop thinking about, the tremor that was his body's commentary on the depth, the body's review of the conditions, the body saying: this is hard. This is harder than you expected. This is the cost.

Mac set down his Tom Clancy. He did not look at Davy. He looked at the wall of the chamber and he said, in his steady voice, the voice that the helium could not alter because the steadiness was not in the frequency but in the rhythm: My first sat, I couldnae sign my name. Literally couldnae write. The superintendent wanted me to sign the dive log and I held the pen and my hand shook and the signature looked like a seismograph. The whole crew saw it. Nobody said a word. I did the dive. By day ten it was gone. By day twenty I'd forgotten it happened.

He picked up his Tom Clancy. He opened it to page 156.

Fraser said, from his bunk, without looking up from the bailout bottle he was unnecessarily inspecting: My second rotation, I threw up for three days. HPNS. The nausea. Couldnae eat, couldnae drink, the lot. The doc put me on cyclizine through the medical lock and I lived on that and dry toast for seventy-two hours and then one morning I woke up and it was gone. Just gone. Like it had never been there.

Tomasz said, from behind his crossword, in the accented English that the helium made almost incomprehensible: In Poland, the old divers say the pressure is testing you. Like an examination. If you pass, you stay. If you fail, you go home. But the failing is not a failure — it is the body saying no, and the body has the right to say no. The body is not wrong to say no.

Sean said nothing. This was remarkable. Sean, who talked the way the ventilation hummed, who had not been silent for a consecutive five minutes in fourteen days, was silent now, and the silence was his contribution, his participation in the moment, his respect for the thing that was happening — five men telling a sixth man that the tremor in his hands was not weakness but physiology, not failure but the body doing what bodies did at fifteen atmospheres, protesting, adapting, finding the line between what it could tolerate and what it could not.

Davy lay in his bunk and held his hands flat against his thighs and listened. The chamber held them all. The pressure held the chamber. The conversation held the space between the men, the space that was usually occupied by the routines — the reading, the talking, the crosswords, the cleaning — and that was now occupied by something different, something that the routine existed to prevent but that the routine could not always prevent, the moment of vulnerability, the moment when the body's limits became visible and the man behind the limits was exposed.

The tremor did not pass that day. It did not pass the next day. On the third day, the nausea arrived — not severely, not the three-day heaving that Fraser had described, but a low-grade queasiness that sat in Davy's stomach like ballast, shifting with every movement, the body protesting the depth through the mechanism of disgust, the ancient response to a toxic environment repurposed by the nervous system to express its displeasure with the pressure.

Gary Hendricks came on the intercom. He asked Davy to report his symptoms. Davy reported — tremor, bilateral, fine motor, worse in the morning, improving through the day. Nausea, mild, continuous, manageable. No headache. No visual disturbance. No myoclonic jerks.

Gary said: The doc wants to see you on camera. Stand in front of the viewport.

Davy stood in front of the chamber's viewport — the small circle of reinforced glass set into the chamber wall through which the surface crew could look in and the divers could look out. The diving physician, a man named Dr. Patterson who was based in Aberdeen and connected to the vessel by video link, examined Davy through the camera that the topside crew held against the viewport — the image transmitted to Patterson's monitor, the doctor assessing the patient through two panes of glass and a satellite connection, the medical examination conducted at a distance that was the inverse of intimacy, the physician unable to touch the patient, unable to take a pulse, unable to feel the tremor, relying instead on the visual data and the reported symptoms and the experience of twenty years of diving medicine.

Patterson's verdict came through the intercom. Mild HPNS. Continue monitoring. No diving until the tremor resolves. Light duties in the chamber. Cyclizine available through the medical lock if the nausea worsens.

No diving. The words sat in the chamber with the weight of a sentence. Davy would not dive until the tremor resolved. Davy would stay in the chamber while the others dived, would lie in his bunk while the bell descended, would wait in the steel tube while the work continued on the sea floor below.

Davy took it. He took it the way the younger divers took the reversals that the industry delivered — with the controlled expression of a man who was learning that the body's cooperation was not guaranteed, that the depth extracted a price, and that the price was not always payable in willingness or skill.

The tremor resolved on the fourth day. The nausea lifted on the fifth. By day nineteen, Davy was diving again — his hands steady on the tools, his movement on the sea floor deliberate and controlled, the HPNS a memory stored in the body the way all lessons were stored, not in the conscious mind but in the tissue, in the cells, in the membranes that had flexed under the pressure and then stabilised and then held.

Kwame watched Davy dive on day nineteen and saw in the young man's movements the particular care of a diver who had been humbled by the depth. Not broken — humbled. The difference was the difference between a weld that cracked and a weld that bent. A crack was a failure, a discontinuity, a point at which the metal could not tolerate the stress and surrendered. A bend was a deformation, a yielding, the metal accepting the load and changing shape to accommodate it, the structure altered but intact, the joint holding.

Davy had bent. Davy had not cracked. And the bending was the thing that would make him a good diver, Kwame thought — not the skill, which could be taught, and not the tolerance, which could be developed, but the bending, the yielding to the depth's authority, the acceptance that the body was not a tool to be overridden but a partner to be negotiated with, the negotiation ongoing, the terms renegotiated with each rotation, each bell run, each breath of heliox at fifteen atmospheres.

Kwame wrote in his notebook that night: Davy's hands stopped shaking today. Four days of tremor, five days of nausea, and then the body found its line and held it. The body adjusted. The body always adjusts, if you give it time. If you do not force it. If you let the cells do their work, the membranes find their flexibility, the nervous system recalibrate to the conditions.

He wrote: The body adjusts. The question I have been avoiding for six years is whether the heart adjusts too. Whether the heart can find its line at the new pressure — the pressure of return, the pressure of presence — the way the neurons find their line at the old pressure, the pressure of the deep. Whether the tremor of going home will resolve the way Davy's tremor resolved — not by force, not by will, but by the body's own accommodation, the slow finding of the frequency at which the shaking stops and the hands are steady and the work can be done.