# Predicted peak expiratory flow (Nunn and Gregg)

Peak expiratory flow

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/peak_expiratory_flow`
HTML: https://magentlab.com/docs/peak-expiratory-flow
Markdown: https://magentlab.com/docs/peak-expiratory-flow.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Compute Nunn and Gregg 1989 predicted peak expiratory flow in L/min from age, sex, and height.

## When to use

When an agent needs the published adult predicted PEF and must not invent a personal-best or action-plan zone.

## When not to use

- Not a personal-best, asthma action-plan zone, or diagnosis of obstruction. Predicted PEF is for adults aged 15-85 as enrolled.
- Does not apply pediatric equations. Does not convert a measured PEF to percent predicted unless the agent supplies the measured value separately.

## Formula

```
ln(PEF_l_min) = a*ln(age) + b*age + c/height_cm + d; male a=0.544 b=-0.0151 c=-74.7 d=5.48; female a=0.376 b=-0.0120 c=-58.8 d=5.63
```

## Citation

[New regression equations for predicting peak expiratory flow in adults](https://doi.org/10.1136/bmj.298.6680.1068)
Nunn AJ, Gregg I
BMJ. 1989;298(6680):1068-1070
DOI: [10.1136/bmj.298.6680.1068](https://doi.org/10.1136/bmj.298.6680.1068)

## Worked example

### 40-year-old man, 175 cm

Given: `age=40, height_cm=175, sex=male`

1. ln(PEF) = 0.544 ln(40) − 0.0151×40 − 74.7/175 + 5.48
2. PEF = exp(ln PEF), rounded to the nearest L/min


### 40-year-old woman, 165 cm

Given: `age=40, height_cm=165, sex=female`

1. ln(PEF) = 0.376 ln(40) − 0.0120×40 − 58.8/165 + 5.63
2. PEF = exp(ln PEF), rounded to the nearest L/min


## Also searched as

- predicted PEF
- peak expiratory flow
- Nunn Gregg PEF
- expected peak flow
- PEFR predicted

## Parameters

- `age` (integer, required): Age in years (integer 15-85). Nunn and Gregg 1989 adult range.
- `sex` (string, required): Sex for the published regression (female or male).
- `height_cm` (number, optional): Height in centimetres (50-250). Provide height_cm or height_in.
- `height_in` (number, optional): Height in inches (20-98). Converted as cm = in × 2.54.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/peak_expiratory_flow`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "age": "40",
      "height_cm": "175",
      "sex": "male"
    },
    {
      "age": "40",
      "height_cm": "175",
      "sex": "male"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/peak-expiratory-flow

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/peak_expiratory_flow",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Nunn AJ, Gregg I",
        "doi": "10.1136/bmj.298.6680.1068",
        "id": "nunn-gregg-1989",
        "source": "BMJ. 1989;298(6680):1068-1070",
        "title": "New regression equations for predicting peak expiratory flow in adults"
      },
      "formula": "nunn_gregg_1989",
      "formula_expression": "ln(PEF_l_min) = a*ln(age) + b*age + c/height_cm + d; male a=0.544 b=-0.0151 c=-74.7 d=5.48; female a=0.376 b=-0.0120 c=-58.8 d=5.63",
      "age_years": 40,
      "sex": "male",
      "height_cm": 175.0,
      "predicted_pef_l_min": 636.0
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Nunn AJ, Gregg I",
        "doi": "10.1136/bmj.298.6680.1068",
        "id": "nunn-gregg-1989",
        "source": "BMJ. 1989;298(6680):1068-1070",
        "title": "New regression equations for predicting peak expiratory flow in adults"
      },
      "formula": "nunn_gregg_1989",
      "formula_expression": "ln(PEF_l_min) = a*ln(age) + b*age + c/height_cm + d; male a=0.544 b=-0.0151 c=-74.7 d=5.48; female a=0.376 b=-0.0120 c=-58.8 d=5.63",
      "age_years": 40,
      "sex": "male",
      "height_cm": 175.0,
      "predicted_pef_l_min": 636.0
    }
  ]
}
```

## Response fields

- `formula` (string): nunn_gregg_1989
- `formula_expression` (string): Exact expression used
- `age_years` (integer): Age used
- `sex` (string): male or female
- `height_cm` (number): Normalized height in cm
- `predicted_pef_l_min` (number): Predicted peak expiratory flow in L/min, nearest litre
- `citation` (object): Nunn and Gregg BMJ 1989 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Nunn AJ, Gregg I",
    "doi": "10.1136/bmj.298.6680.1068",
    "id": "nunn-gregg-1989",
    "source": "BMJ. 1989;298(6680):1068-1070",
    "title": "New regression equations for predicting peak expiratory flow in adults"
  },
  "formula": "nunn_gregg_1989",
  "formula_expression": "ln(PEF_l_min) = a*ln(age) + b*age + c/height_cm + d; male a=0.544 b=-0.0151 c=-74.7 d=5.48; female a=0.376 b=-0.0120 c=-58.8 d=5.63",
  "age_years": 40,
  "sex": "male",
  "height_cm": 175.0,
  "predicted_pef_l_min": 636.0
}
```

## Errors

- HTTP 400 `invalid_peak_flow_age`: age must be an integer from 15 to 85 (Nunn and Gregg 1989). Returned before settlement; you are not charged.
- HTTP 400 `invalid_sex`: sex must be female or male Returned before settlement; you are not charged.
- HTTP 400 `invalid_height`: height_cm (50-250) or height_in (20-98) is required Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [PaO2/FiO2 ratio](https://magentlab.com/docs/pf-ratio) — Compute the PaO2/FiO2 ratio as arterial PO2 in mm Hg divided by inspired oxygen fraction.
- [ROX index](https://magentlab.com/docs/rox) — Compute the ROX index as pulse-oximetry SpO2 percent divided by inspired oxygen fraction, then divided by respiratory rate.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON echoing accepted, payload, and extensions when present).
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.