One of the more difficult concepts in respiratory physiology to grasp is that the fraction of inspired oxygen is the same at all altitudes. It seems counter-intuitive: We know that people get short of breath at altitude because there is "less oxygen," and we instinctively associate "less oxygen" with a decrease in FiO2. But FiO2 is constant at 21% throughout the atmosphere, so what's going on? Partial gas pressures.

A little math is in order here. Outside my window, here around sea level, it's currently 102.0 kPa. 102.0 kPa * 0.21 = 21.42 kPa ppO2. Keep this number in mind. It'll be important later.

Start from the west side of the island. Drive up along highway 19, then turn off on Waikoloa Road. Stop for gas up in Waikoloa Village; try not to be alarmed by the price per gallon. ($3.64 as of January 2008.) Pick up some snacks and drinks at the grocery store, then turn mauka and keep going until you hit highway 190. Follow the signs for Waimea.

About halfway there, you'll see a sign: Saddle Road.

The US Government built this during the second world war. They wanted a fast way to get from one side of the island to the other, and they weren't terribly picky about how it was built. So they cut, cleared, and paved. It used to be that rental car companies wouldn't let you turn right at this intersection, and for good reason. It's a windy, hilly, narrow road, though apparently vastly improved in recent years. In mid-2007 the state opened a new 6.5 mile segment on the Hilo side that is built to current standards, representing some of the nicest road on the island. If you drive Saddle Road from east-to-west, you'll be in for a rude shock after you cross the high mark. If you drive it from west-to-east, it'll be a nice surprise.

This is one of the most sparsely inhabited parts of Hawaii.

Things get interesting the higher you get. The US Army likes it up here. They've got their own airfield, Bradshaw (BSF/PHSF), at 6,190 feet, smack in the middle of the Pohakuloa Training Area. The US military loves Pohakuloa -- it's the only place in the Pacific they can fire their weapons at full-range, with their full destructive power. All varieties of air crews fly sorties over the PTA to practice bombing stuff. Ground forces come over on ships to Kawaihae, then do a road march up the mountain to get to Pohakuloa.

Armored vehicles (and incoming fire) have the right of way on Saddle Road.

At the 28 mile marker, turn left. You'll have to look for it in the fog and mist that is prevalent around this altitude. There's a sign here:

VISITOR INFORMATION
STATION 6 MILES
ALL TRAVELERS STOP THERE FOR
HAZARD INFORMATION

You feel your pulse start to quicken. John A. Burns Way takes you about a third of the way up the mountain, towards the Onizuka Center for International Astronomy. Ellison Onizuka, he of STS-51-L, grew up in Kealakekua, on the west side of the island, and is remembered very fondly here. On your way home, if you're flying out of Keahole, stop by the Onizuka science center on the airport grounds and pay the $3 admission fee to look at artifacts from Ellison's youth, and to stare at Fred Haise's unused EVA suit.

You're at 9,200 feet. This is the Visitor Information Station. If you were to measure your height above the seafloor, you'd be looking 28,200 feet down. The summit of Mt. Everest is at 29,028 feet. Spend at least half an hour here. Breathe deeply. Hydrate. Some people feel nauseous, light headed, or dizzy. Others get exertionally short of breath. There's oxygen inside the VIS if you're really desperate, but a better strategy might be to get off the mountain.

Altitude sickness is usually seen at elevations above 6,500 feet, or atmospheric pressures below 75 kPa. People get headaches, become weak, can't sleep, get paresthesic or edematous. The formal list looks something like this:

• Anorexia, nausea, vomiting
• Fatigue, weakness, general malaise, drowsiness, insomnia
• Dizziness, vertigo
• Exertional shortness of breath
• Peripheral paresthesia or edema
• Tachycardia or tachypnea

The body can acclimatize to this lower pressure. The oxygen partial pressure at this altitude is 15.75 kPa. Over time, 2,3-diphosphoglycerate will shift the oxyhemoglobin dissociation curve to the right, enhancing the release of oxygen in end tissues. Longer term, more erythrocytes and more hemoglobin are produced to help carry oxygen to the cells. This is why athletes train at high elevation, and why you can get in trouble with the doping authorities if your hemoglobin is too high.

Edema is the big worry up at this altitude. It's normal to get some peripheral edema, but when it starts to accumulate in the lungs or, worse, the brain -- it can kill. Leave the mountain immediately. Get off. This isn't a joke.

But if you're doing well, have your breathing under control, and feel OK, maybe you want to think about going up further. You've shopped in the gift shop, you brought the warm clothes you flew over in, you've seen the videos they play, maybe chatted with the rangers about driving up to the summit and what the roads are like. You saw the cannisters of brake fluid and motor oil for sale in the shop. You're confident in your car and your driving ability. So you get back in and point up the mountain, past Hale Pohaku, where the visiting astronomers stay.

The road gets bad almost right away. Four miles of windy washboard road are staring you in the face. Even 20 miles an hour feels too fast. The car is vibrating all over the road. You grip the wheel, part your teeth, stick your tongue out a bit.

The terrain gradually becomes stranger and stranger. NASA brought the Apollo astronauts here.

At 11,300 feet, there's a pull-out. You see something you never thought you'd see at 19N: Snow.

You keep driving. Suddenly it's foggy again, only this time, it's not fog -- it's the clouds you saw from sea level earlier in the morning. Earlier you looked south over Mauna Loa and saw a bank of clouds at your eye level; now, you're in another one. Snow is all around you, copious amounts of snow. This is Hawaii!

Yes, but you're also at 13,760 feet. Most people have never been this high unprotected before.

Around the seven mile mark, you turn a corner, and suddenly, there they are, big as life, like props from a truly strange science fiction movie: The Mauna Kea Observatories. Clouds are below you, the sky is above you. The white and silver domes shine in the sun. Take the right road at the fork, up towards the University of Hawaii telescopes, the United Kingdom Infrared Telescope, Gemini North, and the Canada-France-Hawaii Telescope. Stare at the real summit. Some looney-tunes are busy climbing up towards it. You can only imagine the headaches they must be experiencing. The truly insane can hike from the VIS to the summit in about 10 hours, round trip.

In the winter, ice accumulates on the domes of the telescopes. As the temperature rises, the ice melts, crashing to the ground, sometimes injuring people. It was 82F when you left the beach this morning. The car thermometer now says it is 37F. A strong wind is blowing, making you feel even colder.

Look west. You can see the twin domes of the Keck observatory, the largest optical telescopes in the world, the NASA Infrared Telescope Facility, and Japan's Subaru telescope. Four hours ago, you looked up from the beach and saw these four buildings glistening in the sun, on a field of snow, and now you're here. Moving is difficult -- you're breathing hard. You feel fuzzy, like you didn't get enough sleep last night. Angles don't seem right; depth perception is a little fleeting. You want to have a snowball fight on what feels like the top of the world, but are afraid you might not have the strength to throw anything.

If you had a barometer, it would tell you the atmospheric pressure was 61 kPa. You might have to struggle with the math, but that works out to a ppO2 of 12.81 kPa. This is 60% of the ppO2 at sea level. Your body is trying to cope with 40% less oxygen. No wonder you're tired.

The exotic stuff happens a little lower down. You drive back down the road, carefully, and take the left fork you ignored before. A giant aluminum golf ball shines on your left; you spot a red van with a red beacon on its roof: MAUNA KEA OBSERVATORIES EMERGENCY EVACUATION VEHICLE. This is not a good place to be if it starts to snow.

You're standing in submillimeter valley, amongst instruments designed to look between the far-infrared and microwave parts of the electromagnetic spectrum. These are not the telescopes you think of when you think of telescopes, unless you really like radioastronomy. The Caltech Submillimeter Observatory and the James Clerk Maxwell Telescope, along with the Submillimeter Array do this work. This is one of two places on the planet where you can do this; the other is in Chile. All other research in this part of the spectrum happens in space.

The instruments that do the detecting of these signals have to be cooled to temperatures that are mind-blowing. You remember seeing something back at the VIS that called the JCMT the coldest thing on planet earth.

Liquid helium deliveries to the summit are complicated affairs.

Your head is spinning, and maybe not necessarily from the decreased oxygen available. This is heady stuff -- the science and the connection with the universe. It must be incredible up here at night. The tachypnea is getting noticable now. You start to wonder whether coming up here was such a good idea. Then you see it -- you never expected to see it, and yet, there it is, right in front of you. No one will believe this, will they? It's a hypoxic hallucination. Except... it isn't.

People are skiing down from the summit of Mauna Kea.

You get back in your car, wondering if you're clear-headed enough to make it down the access road. The smooth pavement is inviting, but you keep it slow anyway, nudging the car into first gear and trying to stay off the brake as much as possible. As you descend into the thicker atmosphere, you can feel your head start to clear. You stop at the 11,500 pull-out and check the car out -- the brakes are stinking, hot, but still have enough grab. Your breathing gets easier. The pavement ends soon after, and this time the washboarding is even worse. The car feels like it is going to vibrate off the road. Just when you think the road isn't going to get any better, that you're going to need to take a breather, Hale Pohaku comes into view and then, seconds later, the VIS. You made it.

Keep going down the mountain. Air is warmer down here, thicker, more humid. You'd swear you could feel the increased air pressure on your body, welcoming it back. You turn left off John A. Burns Way and head for Hilo. Back on the nicest roads on the island. You're descending now, heading for sea level in a hurry. The landscape is picking up, the grasses of the west side, and the pine of the mountain giving way to Hilo's lush greenness -- rainforest. The air is moist, delicious.

You suck in as much as you can, marvelling at what you've just been through, and try to remember what it was like to be breathless on the top of the Hawaiian islands, in a place where the stars speak to men...

phloem@fumbling.com